xfs: refactor loading quota inodes in the regular case

xfs: refactor loading quota inodes in the regular case

Create a helper function to load quota inodes in the case where the
dqtype and the sb quota inode fields correspond.  This is true for
nearly all the iget callsites in the quota code, except for when we're
switching the group and project quota inodes.  We'll need this in
subsequent patches to make the metadir handling less convoluted.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>