mfd: Constify i2c_device_id tables

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Harald Welte <laforge@gnumonks.org>
Cc: Matti Aaltonen <matti.j.aaltonen@nokia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/pcf50633-core.c b/drivers/mfd/pcf50633-core.c
index c1306ed..c7687f6 100644
--- a/drivers/mfd/pcf50633-core.c
+++ b/drivers/mfd/pcf50633-core.c
@@ -356,7 +356,7 @@
 	return 0;
 }
 
-static struct i2c_device_id pcf50633_id_table[] = {
+static const struct i2c_device_id pcf50633_id_table[] = {
 	{"pcf50633", 0x73},
 	{/* end of list */}
 };