mn10300: use "#elif defined(CONFIG_*)" instead of "#elif CONFIG_*"

Fix the warnings:

  arch/mn10300/kernel/irq.c:173:7: warning: "CONFIG_MN10300_TTYSM1_TIMER9" is not defined [-Wundef]
  arch/mn10300/kernel/irq.c:175:7: warning: "CONFIG_MN10300_TTYSM1_TIMER3" is not defined [-Wundef]

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>