block: Remove an obsolete comment from sg_io()

Commit b7819b92 ("block: remove the blk_execute_rq return value")
changed the return type of blk_execute_rq() from int into void. That
change made a comment in sg_io() obsolete. Hence remove that comment.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Link: https://lore.kernel.org/r/20210413034142.23460-1-bvanassche@acm.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>