hypervisor: fix riscv clippy lint

In preparation for enabling tools/clippy to check riscv, clean up the
warning in the hypervisor crate.

Change-Id: Iab2d1f703e0ab5e40ed165873376cdfabdc3de60
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4505756
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Dennis Kempin <denniskempin@google.com>

hypervisor/src/kvm/riscv64.rs

@@ -137,7 +137,7 @@ impl VcpuRiscv64 for KvmVcpu {
         if ret == 0 {
             Ok(val)
         } else {
-            return errno_result();
+            errno_result()
         }
     }
 }