The add_new_disk returns with communication locked if
__sendmsg returns failure, fix it with call unlock_comm
before return.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
CC: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>