fs: dlm: fix missing unlock on error in accept_from_sock()

Add the missing unlock before return from accept_from_sock()
in the error handling case.

Fixes: 6cde210a ("fs: dlm: add helper for init connection")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NDavid Teigland <teigland@redhat.com>

fs/dlm/lowcomms.c

@@ -931,6 +931,7 @@ static int accept_from_sock(struct listen_connection *con)
 			result = dlm_con_init(othercon, nodeid);
 			if (result < 0) {
 				kfree(othercon);
+				mutex_unlock(&newcon->sock_mutex);
 				goto accept_err;
 			}