Fix clippy::unnecessary_get_then_check warnings

Avoid .get()ting something just to check if it's present; use
.contains_key() instead (or .entry() in the case where we want to insert
an item if the key is not present).

BUG=b:344974550
TEST=tools/clippy

Change-Id: I78ee9e5a7ad9ffd693d9a50a347663444e1516a2
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5609074
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

devices/src/pci/pcie/pcie_switch.rs

@@ -221,7 +221,7 @@ impl HotPlugBus for PcieDownstreamPort {
         if !self.pcie_port.hotplug_implemented() {
             bail!("hotplug not implemented.");
         }
-        if self.downstream_devices.get(&addr).is_none() {
+        if !self.downstream_devices.contains_key(&addr) {
             bail!("no downstream devices.");
         }
         if !self.pcie_port.is_hotplug_ready() {

devices/src/vfio.rs

@@ -361,7 +361,7 @@ impl VfioContainer {
     }
 
     fn is_group_set(&self, group_id: u32) -> bool {
-        self.groups.get(&group_id).is_some()
+        self.groups.contains_key(&group_id)
     }
 
     fn check_extension(&self, val: IommuType) -> bool {

resources/src/system_allocator.rs

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+use std::collections::btree_map;
 use std::collections::BTreeMap;
 
 use base::pagesize;
@@ -270,36 +271,34 @@ impl SystemAllocator {
     }
 
     fn get_pci_allocator_mut(&mut self, bus: u8) -> Option<&mut AddressAllocator> {
-        // pci root is 00:00.0, Bus 0 next device is 00:01.0 with mandatory function
-        // number zero.
-        if self.pci_allocator.get(&bus).is_none() {
-            let base = if bus == 0 { 8 } else { 0 };
+        match self.pci_allocator.entry(bus) {
+            btree_map::Entry::Occupied(entry) => Some(entry.into_mut()),
+            btree_map::Entry::Vacant(entry) => {
+                // pci root is 00:00.0, Bus 0 next device is 00:01.0 with mandatory function number
+                // zero.
+                let base = if bus == 0 { 8 } else { 0 };
 
-            // Each bus supports up to 32 (devices) x 8 (functions).
-            // Prefer allocating at device granularity (preferred_align = 8), but fall back to
-            // allocating individual functions (min_align = 1) when we run out of devices.
-            match AddressAllocator::new(
-                AddressRange {
-                    start: base,
-                    end: (32 * 8) - 1,
-                },
-                Some(1),
-                Some(8),
-            ) {
-                Ok(v) => self.pci_allocator.insert(bus, v),
-                Err(_) => return None,
-            };
+                // Each bus supports up to 32 (devices) x 8 (functions).
+                // Prefer allocating at device granularity (preferred_align = 8), but fall back to
+                // allocating individual functions (min_align = 1) when we run out of devices.
+                let pci_alloc = AddressAllocator::new(
+                    AddressRange {
+                        start: base,
+                        end: (32 * 8) - 1,
+                    },
+                    Some(1),
+                    Some(8),
+                )
+                .ok()?;
+
+                Some(entry.insert(pci_alloc))
+            }
         }
-        self.pci_allocator.get_mut(&bus)
     }
 
     // Check whether devices exist or not on the specified bus
     pub fn pci_bus_empty(&self, bus: u8) -> bool {
-        if self.pci_allocator.get(&bus).is_none() {
-            true
-        } else {
-            false
-        }
+        !self.pci_allocator.contains_key(&bus)
     }
 
     /// Allocate PCI slot location.