md-cluster: fix potential lock issue in add_new_disk

The add_new_disk returns with communication locked if
__sendmsg returns failure, fix it with call unlock_comm
before return.

Reported-by: Dan Carpenter <[e-mail]>
CC: Goldwyn Rodrigues <[e-mail]>
Signed-off-by: Guoqing Jiang <[e-mail]>
Signed-off-by: Shaohua Li <[e-mail]>

drivers/md/md-cluster.c

···
 	cmsg.raid_slot = cpu_to_le32(rdev->desc_nr);
 	lock_comm(cinfo, 1);
 	ret = __sendmsg(cinfo, &cmsg);
-	if (ret)
+	if (ret) {
+		unlock_comm(cinfo);
 		return ret;
+	}
 	cinfo->no_new_dev_lockres->flags |= DLM_LKF_NOQUEUE;
 	ret = dlm_lock_sync(cinfo->no_new_dev_lockres, DLM_LOCK_EX);
 	cinfo->no_new_dev_lockres->flags &= ~DLM_LKF_NOQUEUE;