NFC: digital: Ensure no NAD byte in DEP_REQ and DEP_RES frames

According to chapter 14 of the NFC-DEP Digital
Protocol Spec., the NAD byte should never be
present in DEP_REQ or DEP_RES frames.  However,
this is not enforced so add that enforcement code.

Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>