Revert "dm raid: fix discard limits for raid1 and raid10"

Revert "dm raid: fix discard limits for raid1 and raid10"

This reverts commit e0910c8e4f87bb9f767e61a778b0d9271c4dc512.

Reverting 6ffeb1c3f822 ("md: change mddev 'chunk_sectors' from int to
unsigned") exposes dm-raid.c compiler warnings detailed that commit's
header. Clearly this more conservative fix, of simply reverting
e0910c8e4f8, would've been more prudent given how late we were in the
v5.10 release. Lessons have been learned.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>