dm: suppress endian warnings

Suppress sparse warnings about cpu_to_le32() by using __le32 types for
on-disk data etc.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --cc drivers/md/dm-crypt.c
Simple merge

diff --cc drivers/md/dm-log.c
Simple merge

diff --cc drivers/md/dm-snap-persistent.c
Simple merge