do_debug() and do_int3() return void.

This patch fixes the CONFIG_KPROBES variant of do_int3() to return void too
and adjusts entry.S accordingly.
Signed-off-by: Stas Sergeev <stsp@aknet.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>