xfs: remove the extsize argument to xfs_eof_alignment

And move the code dependent on it to the one caller that cares
instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>