Even though "we have enough padding that it should be ok", round up the
watermark entries to the next unit to be on the safe side...

v2: Use the DIV_ROUND_UP macro
v3: Spotted a few more missing round-ups.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>