[PATCH v2] iio: adc: viperboard: Fix error handling in vprbrd_iio_read_raw

[Salah Triki <salah.triki@gmail.com>]

The driver proceeds to the reception phase even if the preceding
transmission fails.

This uses a goto error label for an early bail out and ensures the mutex is
properly unlocked in case of failure.

Fixes: ffd8a6e7a778 ("iio: adc: Add viperboard adc driver")
Signed-off-by: Salah Triki <salah.triki@gmail.com>
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Reviewed-by: Maxwell Doose <m32285159@gmail.com>
---
Changes in v2:
  - Add "adc" to the patch title.
  - Move dev_err() out of the mutex critical section.
  - Include Reviewed-by tags from Joshua and Maxwell.

 drivers/iio/adc/viperboard_adc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/viperboard_adc.c b/drivers/iio/adc/viperboard_adc.c
index 9bb0b83c8f67..f7ce3effd730 100644
--- a/drivers/iio/adc/viperboard_adc.c
+++ b/drivers/iio/adc/viperboard_adc.c
@@ -70,8 +70,10 @@ static int vprbrd_iio_read_raw(struct iio_dev *iio_dev,
 			VPRBRD_USB_TYPE_OUT, 0x0000, 0x0000, admsg,
 			sizeof(struct vprbrd_adc_msg), VPRBRD_USB_TIMEOUT_MS);
 		if (ret != sizeof(struct vprbrd_adc_msg)) {
-			dev_err(&iio_dev->dev, "usb send error on adc read\n");
 			error = -EREMOTEIO;
+			mutex_unlock(&vb->lock);
+			dev_err(&iio_dev->dev, "usb send error on adc read\n");
+			goto error;
 		}
 
 		ret = usb_control_msg(vb->usb_dev,
-- 
2.43.0