net: dsa: microchip: fix Clang -Wunused-const-variable warning on 'ksz_dt_ids'

This patch removes the of_match_ptr() pointer when dereferencing the
ksz_dt_ids which produce the unused variable warning.

Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>