[spinel] fix error code when waiting rcp response timeout (#9278)

For the RCP waiting response timeout handle logic, the error code of
processing `WaitResponse()` will be checked, if there is no error, the
function `ResetRcp` will return with a log "Software reset RCP
successfully". But the implementation of the `WaitResponse` it will
always return OT_ERROR_NONE even if waiting response timeout.

This commit returns `OT_ERROR_RESPONSE_TIMEOUT` on response timeout.

src/lib/spinel/radio_spinel_impl.hpp

@@ -1500,7 +1500,7 @@ template <typename InterfaceType> otError RadioSpinel<InterfaceType>::WaitRespon
             {
                 HandleRcpTimeout();
             }
-            ExitNow(mError = OT_ERROR_NONE);
+            ExitNow(mError = OT_ERROR_RESPONSE_TIMEOUT);
         }
     } while (mWaitingTid || !mIsReady);