trivial: cleanup hpfall example code (checkpatch)

This patch makes hpfall.c conform to kernel coding style.

I have not fixed the C99 // comments on two lines as they
help indicate that those are not actually comments but
incomplete code.

Before:
 total: 10 errors, 6 warnings, 101 lines checked
After:
 total: 2 errors, 0 warnings, 99 lines checked

Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>