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 <[e-mail]>
Signed-off-by: George McCollister <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/dsa/xrs700x/xrs700x_i2c.c

···
 
 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

···
 	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 },