media: atmel: atmel-sama7g5-isc: fix warning in configs without OF

All warnings (new ones prefixed by >>):

>> drivers/media/platform/atmel/atmel-sama7g5-isc.c:610:34: warning: unused variable 'microchip_xisc_of_match' [-Wunused-const-variable]
   static const struct of_device_id microchip_xisc_of_match[] = {
                                    ^
   13 warnings generated.

vim +/microchip_xisc_of_match +610 drivers/media/platform/atmel/atmel-sama7g5-isc.c

   609
 > 610  static const struct of_device_id microchip_xisc_of_match[] = {
   611          { .compatible = "microchip,sama7g5-isc" },
   612          { }
   613  };
   614  MODULE_DEVICE_TABLE(of, microchip_xisc_of_match);
   615

Fixed warning by guarding the atmel_isc_of_match by CONFIG_OF.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: c9aa9738 ("media: atmel: atmel-isc: add microchip-xisc driver")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>