gpu: ion: Fix bug in ion_free

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -406,6 +406,7 @@ void ion_free(struct ion_client *client, struct ion_handle *handle)
 
 	if (!valid_handle) {
 		WARN(1, "%s: invalid handle passed to free.\n", __func__);
+		mutex_unlock(&client->lock);
 		return;
 	}
 	ion_handle_put(handle);