block: use the right type for stub rq_integrity_vec()

commit 69b65176 upstream.

For !CONFIG_BLK_DEV_INTEGRITY, rq_integrity_vec() wasn't updated
properly. Fix it up.

Fixes: cf546dd2 ("block: change rq_integrity_vec to respect the iterator")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Cc: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>