[PATCH] m32r: Fix "value computed not used" warnings

Fix to remove annoying gcc-4.1 warnings "value computed not used" for m32r;
Modify set_mb to cast to void for SMP.

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>