block: Fix the bio.bi_opf comment

block: Fix the bio.bi_opf comment

[ Upstream commit 46880416c06fb6239f7dcbaf3c528507fa8fc9d4 ]

Commit 86207eb9fda1 modified the Linux kernel such that the bottom bits
of the bi_opf member contain the operation instead of the topmost bits.
That commit did not update the comment next to bi_opf. Hence this patch.

From commit 86207eb9fda1:
-#define bio_op(bio)    ((bio)->bi_opf >> BIO_OP_SHIFT)
+#define bio_op(bio)    ((bio)->bi_opf & REQ_OP_MASK)

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Fixes: 86207eb9fda1 ("block: better op and flags encoding")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220511235152.1082246-1-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>