drivers: uio: Fix UIO device registration failure

Until recently uio_get_minor() returned 0 for success and
a negative value on failure.  This became non-negative for suceess and
negative for failure.  Restore the original return value spec so that we can
successfully initialize UIO devices with a non-zero minor device
number.

Cc: "Hans J. Koch" <hjk@hansjkoch.de>
Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio.c

@@ -374,6 +374,7 @@ static int uio_get_minor(struct uio_device *idev)
 	retval = idr_alloc(&uio_idr, idev, 0, UIO_MAX_DEVICES, GFP_KERNEL);
 	if (retval >= 0) {
 		idev->minor = retval;
+		retval = 0;
 	} else if (retval == -ENOSPC) {
 		dev_err(idev->dev, "too many uio devices\n");
 		retval = -EINVAL;