gpio: xilinx: Make of_device_id array const

Make of_device_id array const, because all OF functions
handle it as const.

Signed-off-by: Jingoo Han <[e-mail]>
Reviewed-by: Michal Simek <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-xilinx.c

···
 	return 0;
 }
 
-static struct of_device_id xgpio_of_match[] = {
+static const struct of_device_id xgpio_of_match[] = {
 	{ .compatible = "xlnx,xps-gpio-1.00.a", },
 	{ /* end of list */ },
 };