[XFS] replace "extern inline" with "static inline" Patch from Adrian Bunk

<bunk@stusta.de>, thanks a lot!

SGI-PV: 942227
SGI-Modid: xfs-linux:xfs-kern:198642a

Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>