greybus: connection: protocol can be NULL in gb_connection_exit()

gb_connection_exit() is getting called from gb_connection_destroy() now,
which will get called from failure path of gb_connection_create_range()
(in a later commit). And at that point connection->protocol will be
NULL.

Don't print an error message if this happens in gb_connection_exit().
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>

drivers/staging/greybus/connection.c

@@ -396,10 +396,8 @@ static int gb_connection_init(struct gb_connection *connection)
 
 static void gb_connection_exit(struct gb_connection *connection)
 {
-	if (!connection->protocol) {
-		dev_warn(&connection->dev, "exit without protocol.\n");
+	if (!connection->protocol)
 		return;
-	}
 
 	spin_lock_irq(&connection->lock);
 	if (connection->state != GB_CONNECTION_STATE_ENABLED) {