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>

virtio-devices/src/vsock/device.rs

@@ -355,11 +355,9 @@ where
         }
     }
 
-    fn set_state(&mut self, state: &VsockState) -> io::Result<()> {
+    fn set_state(&mut self, state: &VsockState) {
         self.common.avail_features = state.avail_features;
         self.common.acked_features = state.acked_features;
-
-        Ok(())
     }
 }
 
@@ -531,9 +529,8 @@ where
                 }
             };
 
-            return self.set_state(&vsock_state).map_err(|e| {
-                MigratableError::Restore(anyhow!("Could not restore VSOCK state {:?}", e))
-            });
+            self.set_state(&vsock_state);
+            return Ok(());
         }
 
         Err(MigratableError::Restore(anyhow!(