xfs: merge xfs_qm_export_dquot into xfs_qm_scall_getquota

The is no good reason to have these two separate, and for the next change
we would need the full struct xfs_dquot in xfs_qm_export_dquot, so better
just fold the code now instead of changing it spuriously.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>