LU-5463 osc: update kms in brw_interpret() properly

LU-5463 osc: update kms in brw_interpret() properly

In brw_interpret(), we forgot page offset when calculating
write offset, that leads to wrong kms for sync write.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I9be90fefa384f9738c11737580637bcec96e5126
Reviewed-on: http://review.whamcloud.com/11374
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Li Dongyang <dongyang.li@anu.edu.au>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>