net: ax88796c: hide ax88796c_dt_ids if !CONFIG_OF

net: ax88796c: hide ax88796c_dt_ids if !CONFIG_OF

Build bot says:

>> drivers/net/ethernet/asix/ax88796c_main.c:1116:34: warning: unused variable 'ax88796c_dt_ids' [-Wunused-const-variable]
   static const struct of_device_id ax88796c_dt_ids[] = {
                                    ^

The only reference to this array is wrapped in of_match_ptr().

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 9c16820e2f08 ("net: ax88796c: ASIX AX88796C SPI Ethernet Adapter Driver")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>