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: a97c69ba ("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>

drivers/net/ethernet/asix/ax88796c_main.c

@@ -1114,11 +1114,13 @@ static int ax88796c_remove(struct spi_device *spi)
 	return 0;
 }
 
+#ifdef CONFIG_OF
 static const struct of_device_id ax88796c_dt_ids[] = {
 	{ .compatible = "asix,ax88796c" },
 	{},
 };
 MODULE_DEVICE_TABLE(of, ax88796c_dt_ids);
+#endif
 
 static const struct spi_device_id asix_id[] = {
 	{ "ax88796c", 0 },