xfs: mark xfs_qm_quotacheck as static

xfs_qm_quotacheck() is not used outside of xfs_qm.c.  Mark it static
and move it around in the file to avoid a forward declaration.

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