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>

vmm/src/lib.rs

@@ -539,10 +539,10 @@ impl Vmm {
         }
     }
 
-    fn vmm_ping(&self) -> result::Result<VmmPingResponse, ApiError> {
-        Ok(VmmPingResponse {
+    fn vmm_ping(&self) -> VmmPingResponse {
+        VmmPingResponse {
             version: self.version.clone(),
-        })
+        }
     }
 
     fn vm_delete(&mut self) -> result::Result<(), VmError> {
@@ -1205,9 +1205,9 @@ impl Vmm {
                                     sender.send(response).map_err(Error::ApiResponseSend)?;
                                 }
                                 ApiRequest::VmmPing(sender) => {
-                                    let response = self.vmm_ping().map(ApiResponsePayload::VmmPing);
+                                    let response = ApiResponsePayload::VmmPing(self.vmm_ping());
 
-                                    sender.send(response).map_err(Error::ApiResponseSend)?;
+                                    sender.send(Ok(response)).map_err(Error::ApiResponseSend)?;
                                 }
                                 ApiRequest::VmPause(sender) => {
                                     let response = self