build: Remove unnecessary Result<> returns

If the function can never return an error this is now a clippy failure:

error: this function's return value is unnecessarily wrapped by `Result`
   --> virtio-devices/src/watchdog.rs:215:5
    |
215 | /     fn set_state(&mut self, state: &WatchdogState) -> io::Result<()> {
216 | |         self.common.avail_features = state.avail_features;
217 | |         self.common.acked_features = state.acked_features;
218 | |         // When restoring enable the watchdog if it was previously enabled. We reset the timer
...   |
223 | |         Ok(())
224 | |     }
    | |_____^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_wraps

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

hypervisor/src/mshv/mod.rs

@@ -144,9 +144,8 @@ impl SoftTLB {
     }
 
     // Adds a gva -> gpa mapping into the TLB.
-    fn add_mapping(&mut self, gva: u64, gpa: u64) -> Result<(), PlatformError> {
+    fn add_mapping(&mut self, gva: u64, gpa: u64) {
         *self.addr_map.entry(gva).or_insert(gpa) = gpa;
-        Ok(())
     }
 
     // Do the actual gva -> gpa translation
@@ -383,8 +382,7 @@ impl cpu::Vcpu for MshvVcpu {
                     // Add the GVA <-> GPA mapping.
                     context
                         .tlb
-                        .add_mapping(info.guest_virtual_address, info.guest_physical_address)
-                        .map_err(|e| cpu::HypervisorCpuError::RunVcpu(e.into()))?;
+                        .add_mapping(info.guest_virtual_address, info.guest_physical_address);
 
                     // Create a new emulator.
                     let mut emul = Emulator::new(&mut context);