[XFS] Need to be able to reset sb_qflags if not mounting with quotas

having previously mounted with quotas.

SGI-PV: 940491
SGI-Modid: xfs-linux:xfs-kern:23388a

Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>