LU-13191 osp: handle -EROFS in osp_sync_interpret()

LU-13191 osp: handle -EROFS in osp_sync_interpret()

Upon OST disk failure, osp_sync_interpret() may get -EROFS,
which is a valid errno.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I5c3cff3019aa47c6d5803f0f0b373bc704f18118
Reviewed-on: https://review.whamcloud.com/37404
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>