iscsi-target: remove unnecessary check in iscsit_setup_np error path

Found by coverity.  At this point sock is non-NULL, so the check
to unnecessary.
Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_login.c

@@ -978,7 +978,6 @@ int iscsit_setup_np(
 	return 0;
 fail:
 	np->np_socket = NULL;
-	if (sock)
 	sock_release(sock);
 	return ret;
 }