staging/lustre/lov: calculate file offset correctly

In lov_stripe_pgoff(), it calls lov_stripe_size() to calculate the
file size by ost_size, which will be wrong if the stripe_index
happens to be stripe aligned.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: http://review.whamcloud.com/14462
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6482


Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>