net: dsa: xrs700x: fix unused warning for of_device_id

Fix unused variable warning that occurs when CONFIG_OF isn't defined by
adding __maybe_unused.

>> drivers/net/dsa/xrs700x/xrs700x_i2c.c:127:34: warning: unused
variable 'xrs700x_i2c_dt_ids' [-Wunused-const-variable]
   static const struct of_device_id xrs700x_i2c_dt_ids[] = {
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: George McCollister <george.mccollister@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/xrs700x/xrs700x_i2c.c

@@ -121,7 +121,7 @@ static const struct i2c_device_id xrs700x_i2c_id[] = {
 
 MODULE_DEVICE_TABLE(i2c, xrs700x_i2c_id);
 
-static const struct of_device_id xrs700x_i2c_dt_ids[] = {
+static const struct of_device_id __maybe_unused xrs700x_i2c_dt_ids[] = {
 	{ .compatible = "arrow,xrs7003e", .data = &xrs7003e_info },
 	{ .compatible = "arrow,xrs7003f", .data = &xrs7003f_info },
 	{ .compatible = "arrow,xrs7004e", .data = &xrs7004e_info },

drivers/net/dsa/xrs700x/xrs700x_mdio.c

@@ -138,7 +138,7 @@ static void xrs700x_mdio_remove(struct mdio_device *mdiodev)
 	xrs700x_switch_remove(priv);
 }
 
-static const struct of_device_id xrs700x_mdio_dt_ids[] = {
+static const struct of_device_id __maybe_unused xrs700x_mdio_dt_ids[] = {
 	{ .compatible = "arrow,xrs7003e", .data = &xrs7003e_info },
 	{ .compatible = "arrow,xrs7003f", .data = &xrs7003f_info },
 	{ .compatible = "arrow,xrs7004e", .data = &xrs7004e_info },