[XFS] Fix quotaon syscall failures for group enforcement requests.

xfs_qm_scall_quotaon was incorrectly failing requests to enable group
quota enforcement. Fixes logic error in OQUOTA handling.

SGI-PV: 961964
SGI-Modid: xfs-linux-melb:xfs-kern:28227a

Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>