xfs: move and rename xfs_inode_free_quota_blocks to avoid conflicts

Move this function further down in the file so that later cleanups won't
have to declare static functions.  Change the name because we're about
to rework all the code that performs garbage collection of speculatively
allocated file blocks.  No functional changes.

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