dm: suppress endian warnings

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

Change-Id: I999de9d2966d16cebe8a06a226c02f2785f95927
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Merge "dm: suppress endian warnings" into du44