include/linux/compat.h: coding-style fixes

I touched this file when adding support for the "tilegx" sub-architecture,
and Andrew Morton observed "The file's a mismash of old-style, wrong-style
and right-style.  There's no point in doing mishmash preservation!
May as well fix things up when we touch them."

Accordingly, this change makes <linux/compat.h> as checkpatch-clean
as possible.  It makes no semantic changes whatsoever.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>