dm-integrity: fix mismatched queue limits

dm-integrity: fix mismatched queue limits

A user can integritysetup a device with a backing device using a 4k
logical block size, but request the dm device use 1k or 2k. This
mismatch creates an inconsistency such that the dm device would report
limits for IO that it can't actually execute. Fix this by using the
backing device's limits if they are larger.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>