iio: adc: ad9361: fix possible '-Wuninitialized'

'val' could be used uninitialized in case the 'default' branch is taken.
It's not a real issue since 'ret < 0 ? ret : ...' would still make it
right but let's make the compiler happy by initializing the variable.

Signed-off-by: Nuno Sa <[email protected]>

drivers/iio/adc/ad9361.c

@@ -7811,7 +7811,7 @@ static ssize_t ad9361_phy_tx_read(struct iio_dev *indio_dev,
 {
 	struct ad9361_rf_phy *phy = iio_priv(indio_dev);
 	u8 reg_val_buf[3];
-	u32 val;
+	u32 val = 0;
 	int ret;
 
 	mutex_lock(&phy->lock);