nfc: constify nci_ops

The struct nci_ops is modified by NFC core in only one case:
nci_allocate_device() receives too many proprietary commands (prop_ops)
to configure.  This is a build time known constrain, so a graceful
handling of such case is not necessary.

Instead, fail the nci_allocate_device() and add BUILD_BUG_ON() to places
which set these.

This allows to constify the struct nci_ops (consisting of function
pointers) for correctness and safety.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>