LU-4937 osc: get rid of old checksum initial value

Old code residue assumes initial checksum value as ~0, and relies on
that to check whether OST server has calculated bulk data checksum.
That is not the case anymore.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I99779eaf02d22b470978448ad3f17b35f0e9a475
Reviewed-on: http://review.whamcloud.com/10354
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>