LU-14337 lov: return stripe_count=1 instead of 0 for DoM files

LU-14337 lov: return stripe_count=1 instead of 0 for DoM files

Return stripe_count=1 instead of 0 for DoM files to avoid
divide-by-zero for older userspace that calls this ioctl,
e.g. lustre ADIO driver.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I43c5e01bdee834f9a05a669a3e6f3d5cd926cb87
Reviewed-on: https://review.whamcloud.com/41265
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>