iio: meter: ade7754: add error handling in _reset and _stop_device

This patch adds the error handling for the value returned from
ade7754_spi_read_reg_8. With this patch, the following randconfig
warnings get fixed automatically.

drivers/staging/iio/meter/ade7754.c:222:6: warning: ‘val’ may be used
uninitialized in this function [-Wmaybe-uninitialized]
drivers/staging/iio/meter/ade7754.c:368:6: warning: ‘val’ may be used
uninitialized in this function [-Wmaybe-uninitialized]

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/meter/ade7754.c

@@ -216,9 +216,13 @@ error_ret:
 
 static int ade7754_reset(struct device *dev)
 {
+	int ret;
 	u8 val;
 
-	ade7754_spi_read_reg_8(dev, ADE7754_OPMODE, &val);
+	ret = ade7754_spi_read_reg_8(dev, ADE7754_OPMODE, &val);
+	if (ret < 0)
+		return ret;
+
 	val |= 1 << 6; /* Software Chip Reset */
 	return ade7754_spi_write_reg_8(dev, ADE7754_OPMODE, val);
 }
@@ -362,9 +366,16 @@ error_ret:
 /* Power down the device */
 static int ade7754_stop_device(struct device *dev)
 {
+	int ret;
 	u8 val;
 
-	ade7754_spi_read_reg_8(dev, ADE7754_OPMODE, &val);
+	ret = ade7754_spi_read_reg_8(dev, ADE7754_OPMODE, &val);
+	if (ret < 0) {
+		dev_err(dev, "unable to power down the device, error: %d",
+			ret);
+		return ret;
+	}
+
 	val |= 7 << 3;  /* ADE7754 powered down */
 	return ade7754_spi_write_reg_8(dev, ADE7754_OPMODE, val);
 }