nfc: add missing attribute validation for vendor subcommand

Add missing attribute validation for vendor subcommand attributes
to the netlink policy.

Fixes: 9e58095f ("NFC: netlink: Implement vendor command support")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>