[XFS] Remove useless whitespace in function prototypes

Makes it simpler to annotate function prototypes with __must_check via sed
scripts.

SGI-PV: 980084
SGI-Modid: xfs-linux-melb:xfs-kern:30781a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>