staging: lustre: lov: refactor lov_object_fiemap()

Add fiemap_for_stripe() to get file map extent from each stripe
device.
Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8773
Reviewed-on: https://review.whamcloud.com/23461Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>