iio: meter: ade7759: add error handling in _reset and _stop_device

This patch adds the error handling for the value returned from
ade7759_spi_read_reg_16. With this patch, the following randconfig
warnings get fixed automatically.

drivers/staging/iio/meter/ade7759.c:224:6: warning: ‘val’ may be
used uninitialized in this function [-Wmaybe-uninitialized]
drivers/staging/iio/meter/ade7759.c:309:6: 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/ade7759.c

@@ -218,9 +218,12 @@ static int ade7759_reset(struct device *dev)
 	int ret;
 	u16 val;
 
-	ade7759_spi_read_reg_16(dev,
+	ret = ade7759_spi_read_reg_16(dev,
 			ADE7759_MODE,
 			&val);
+	if (ret < 0)
+		return ret;
+
 	val |= 1 << 6; /* Software Chip Reset */
 	ret = ade7759_spi_write_reg_16(dev,
 			ADE7759_MODE,
@@ -301,11 +304,18 @@ error_ret:
 /* Power down the device */
 static int ade7759_stop_device(struct device *dev)
 {
+	int ret;
 	u16 val;
 
-	ade7759_spi_read_reg_16(dev,
+	ret = ade7759_spi_read_reg_16(dev,
 			ADE7759_MODE,
 			&val);
+	if (ret < 0) {
+		dev_err(dev, "unable to power down the device, error: %d\n",
+			ret);
+		return ret;
+	}
+
 	val |= 1 << 4;  /* AD converters can be turned off */
 
 	return ade7759_spi_write_reg_16(dev, ADE7759_MODE, val);