NFC: trf7970a: Remove useless comment

The last entry in the trf7970a_of_match[] table must be an empty
entry to demarcate the end of the table.  Currently, there is a
comment indicating this but it is obvious so remove the comment.

Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>