NFC: trf7970a: Enable pins are active high not active low

The example DTS code for the trf7970a sets the GPIOs for the EN
and EN2 pins to active low when they are really active high so
correct the error.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>