rtc: constify i2c_device_id

i2c_device_id are not supposed to change at runtime. All functions
working with i2c_device_id provided by <linux/i2c.h> work with
const i2c_device_id. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/rtc-max6900.c b/drivers/rtc/rtc-max6900.c
index 48b6b41..cbdc86a 100644
--- a/drivers/rtc/rtc-max6900.c
+++ b/drivers/rtc/rtc-max6900.c
@@ -226,7 +226,7 @@ max6900_probe(struct i2c_client *client, const struct i2c_device_id *id)
 	return 0;
 }
 
-static struct i2c_device_id max6900_id[] = {
+static const struct i2c_device_id max6900_id[] = {
 	{ "max6900", 0 },
 	{ }
 };