LU-5459 lov: adjust page bufsize after layout change

LU-5459 lov: adjust page bufsize after layout change

Otherwise, the coh_page_bufsize keeps increasing when the file's
layout keeps changing in lov_init_raid0().

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I70066b916d72aabe0349a1faec65eff160e9cf04
Reviewed-on: http://review.whamcloud.com/11394
Reviewed-by: frank zago <fzago@cray.com>
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>