mfd: Constify WM8994 regulator_init_data

The driver has no need to modify the regulator_init_data so declare it
const to allow machine code to do so.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>

include/linux/mfd/wm8994/pdata.h

@@ -23,7 +23,7 @@ struct wm8994_ldo_pdata {
 	int enable;
 
 	const char *supply;
-	struct regulator_init_data *init_data;
+	const struct regulator_init_data *init_data;
 };
 
 #define WM8994_CONFIGURE_GPIO 0x10000