xfs: fix uflags detection at xfs_fs_rm_xquota

We are intended to check up uflags against FS_PROJ_QUOTA rather than
FS_USER_UQUOTA once more, it looks to me like a typo, but might cause
the project quota metadata space can not be removed.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>