osd: PG:: fix, update info_struct_v when _wirte_info

when _write_info, info_struct_v is passed by value, therefore, it just updates local value of info_struct_v. Since info_struct_v in pg is not updated and always be zero,  which will lead to unneccessary update for pg_biginfo before the next time osd daemon restarts.  Fix is passed info_struct_v by reference

Signed-off-by: Ning Yao <zay11022@gmail.com>