serial: core: Don't drop port_mutex in serial_core_remove_one_port

Commit 84a9582f ("serial: core: Start managing serial controllers to
enable runtime PM") required the caller to hold port_mutex rather than
taking it locally. However the mutex_unlock() call wasn't removed
causing the mutex to be dropped unexpectly. Remove the call to
mutex_unlock() (and fix up the early return) to restore correct
behaviour.

Fixes: 84a9582f ("serial: core: Start managing serial controllers to enable runtime PM")
Signed-off-by: Steven Price <steven.price@arm.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230601105548.29965-1-steven.price@arm.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -3194,7 +3194,7 @@ static void serial_core_remove_one_port(struct uart_driver *drv,
 
 	if (!uart_port) {
 		mutex_unlock(&port->mutex);
-		goto out;
+		return;
 	}
 	mutex_unlock(&port->mutex);
 
@@ -3234,8 +3234,6 @@ static void serial_core_remove_one_port(struct uart_driver *drv,
 	wait_event(state->remove_wait, !atomic_read(&state->refcount));
 	state->uart_port = NULL;
 	mutex_unlock(&port->mutex);
-out:
-	mutex_unlock(&port_mutex);
 }
 
 /**