Clarify the control flow in xfs_dialloc. Factor out a helper to go to the
next node from the current one and improve the control flow by expanding
composite if statements and using gotos.
The xfs_ialloc_next_rec helper is borrowed from Dave Chinners dynamic
allocation policy patches.
Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Alex Elder <aelder@sgi.com> Signed-off-by: Felix Blyakher <felixb@sgi.com>