ceph: fix leak of mon authorizer

Fix leak of a struct ceph_buffer on umount.

Signed-off-by: Sage Weil <[e-mail]>

fs/ceph/auth_x.c

···
 		remove_ticket_handler(ac, th);
 	}
 
+	if (xi->auth_authorizer.buf)
+		ceph_buffer_put(xi->auth_authorizer.buf);
+
 	kfree(ac->private);
 	ac->private = NULL;
 }