Set ret to 0 after the initial permission checks to avoid leaking -EPERM
for commands without data transfer.

Link: https://lore.kernel.org/r/20210731074027.1185545-3-hch@lst.de
Fixes: 75ca5640 ("scsi: bsg: Move the whole request execution into the SCSI/transport handlers")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>