rbd: delete an unnecessary check before rbd_dev_destroy()

The rbd_dev_destroy() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 81ea69f..4a87678 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5185,8 +5185,7 @@
 
 out_err:
 	rbd_dev_unparent(rbd_dev);
-	if (parent)
-		rbd_dev_destroy(parent);
+	rbd_dev_destroy(parent);
 	return ret;
 }