LU-11700 osp: GPF in osp_reserved_mb_low_seq_write()

LU-11700 osp: GPF in osp_reserved_mb_low_seq_write()

opd_pre pointer may be uninitialized on statrup

Change-Id: If6ff4289545503e07719c7e9a282be1bd393465b
Cray-bug-id: LUS-6118
Signed-off-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Reviewed-on: https://review.whamcloud.com/33717
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>