power: constify of_device_id array

of_device_id is always used as const.
(See driver.of_match_table and open firmware functions)

Signed-off-by: Fabian Frederick <fabf@skynet.be>

[for vexpress]
Acked-by: Sudeep Holla <sudeep.holla@arm.com>

Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/power/reset/at91-poweroff.c

@@ -140,7 +140,7 @@ static int at91_poweroff_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static struct of_device_id at91_poweroff_of_match[] = {
+static const struct of_device_id at91_poweroff_of_match[] = {
 	{ .compatible = "atmel,at91sam9260-shdwc", },
 	{ .compatible = "atmel,at91sam9rl-shdwc", },
 	{ .compatible = "atmel,at91sam9x5-shdwc", },