nfc: add missing attribute validation for SE API

Add missing attribute validation for NFC_ATTR_SE_INDEX
to the netlink policy.

Fixes: 5ce3f32b ("NFC: netlink: SE API implementation")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>