Smack: fix dereferenced before check

This patch fixes the warning reported by smatch:
security/smack/smack_lsm.c:2872 smack_socket_connect() warn:
variable dereferenced before check 'sock->sk' (see line 2869)

Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>