xfs: make symbols static

Instead of the keyword 'static' the macro 'STATIC' is used, so the
symbols are still global with CONFIG_XFS_DEBUG.

Fix this sparse warnings:
  fs/xfs/linux-2.6/xfs_super.c:638:1: warning: symbol 'xfs_blkdev_get' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_super.c:655:1: warning: symbol 'xfs_blkdev_put' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_super.c:876:1: warning: symbol 'xfsaild' was not declared. Should it be static?
  fs/xfs/xfs_bmap.c:6208:1: warning: symbol 'xfs_check_block' was not declared. Should it be static?
  fs/xfs/xfs_dir2_leaf.c:553:1: warning: symbol 'xfs_dir2_leaf_check' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Felix Blyakher <felixb@sgi.com>