drm: i2c: tda998x: 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: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1503167300-17334-4-git-send-email-arvind.yadav.cs@gmail.com
Link: https://patchwork.freedesktop.org/patch/msgid/60db0ba6ddce08444299533e97c9adec3b3ef1bb.1503311145.git.arvind.yadav.cs@gmail.com

drivers/gpu/drm/i2c/tda998x_drv.c

@@ -1746,7 +1746,7 @@ static const struct of_device_id tda998x_dt_ids[] = {
 MODULE_DEVICE_TABLE(of, tda998x_dt_ids);
 #endif
 
-static struct i2c_device_id tda998x_ids[] = {
+static const struct i2c_device_id tda998x_ids[] = {
 	{ "tda998x", 0 },
 	{ }
 };