mfd: max8997: Make of_device_id array const

Array of struct of_device_id may be be const as expected by both
of_match_table field and of_match_node() call.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/max8997.c

···
 };
 
 #ifdef CONFIG_OF
-static struct of_device_id max8997_pmic_dt_match[] = {
+static const struct of_device_id max8997_pmic_dt_match[] = {
 	{ .compatible = "maxim,max8997-pmic", .data = (void *)TYPE_MAX8997 },
 	{},
 };