ab8500-charger: Check return value of regulator_enable

Check the return value of regulator_enable to silence the following
type of warnings:
drivers/power/ab8500_charger.c:1390:20: warning: ignoring return value
of ‘regulator_enable’, declared with attribute warn_unused_result
[-Wunused-result]
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>

drivers/power/ab8500_charger.c

@@ -1387,8 +1387,12 @@ static int ab8500_charger_ac_en(struct ux500_charger *charger,
 		 * the GPADC module independant of the AB8500 chargers
 		 */
 		if (!di->vddadc_en_ac) {
-			regulator_enable(di->regu);
-			di->vddadc_en_ac = true;
+			ret = regulator_enable(di->regu);
+			if (ret)
+				dev_warn(di->dev,
+					"Failed to enable regulator\n");
+			else
+				di->vddadc_en_ac = true;
 		}
 
 		/* Check if the requested voltage or current is valid */
@@ -1556,8 +1560,12 @@ static int ab8500_charger_usb_en(struct ux500_charger *charger,
 		 * the GPADC module independant of the AB8500 chargers
 		 */
 		if (!di->vddadc_en_usb) {
-			regulator_enable(di->regu);
-			di->vddadc_en_usb = true;
+			ret = regulator_enable(di->regu);
+			if (ret)
+				dev_warn(di->dev,
+					"Failed to enable regulator\n");
+			else
+				di->vddadc_en_usb = true;
 		}
 
 		/* Enable USB charging */