NFC: use kfree_skb() for sk_buffs

This is a struct sk_buff pointer and it should be freed with kfree_skb()
instead of kfree().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>