staging: ste_rmi4: Suppress 'ignoring return value of ‘regulator_enable()' warning

drivers/staging/ste_rmi4/synaptics_i2c_rmi4.c:
        In function ‘synaptics_rmi4_resume’:
drivers/staging/ste_rmi4/synaptics_i2c_rmi4.c:1090:18:
        warning: ignoring return value of ‘regulator_enable’, declared
        with attribute warn_unused_result [-Wunused-result

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: devel@driverdev.osuosl.org
Acked-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ste_rmi4/synaptics_i2c_rmi4.c

@@ -1087,7 +1087,11 @@ static int synaptics_rmi4_resume(struct device *dev)
 	unsigned char intr_status;
 	struct synaptics_rmi4_data *rmi4_data = dev_get_drvdata(dev);
 
-	regulator_enable(rmi4_data->regulator);
+	retval = regulator_enable(rmi4_data->regulator);
+	if (retval) {
+		dev_err(dev, "Regulator enable failed (%d)\n", retval);
+		return retval;
+	}
 
 	enable_irq(rmi4_data->i2c_client->irq);
 	rmi4_data->touch_stopped = false;