osd/HitSet: fix units passed down to bloom's compress()

As of f45c3b98d3941c242d428c971b494fdc5216bd18 this takes a ratio instead
of a percentage.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/HitSet: rename optimize -> seal

Signed-off-by: Sage Weil <sage@inktank.com>