fs: Mark functions as static in exofs/ore_raid.c

Mark functions as static in exofs/ore_raid.c because they are not used
outside this file.

This also eliminates the following warning in exofs/ore_raid.c:
fs/exofs/ore_raid.c:24:14: warning: no previous prototype for _raid_page_alloc [-Wmissing-prototypes]
fs/exofs/ore_raid.c:29:6: warning: no previous prototype for _raid_page_free [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>