mn10300: kernel/internal.h needs <linux/irqreturn.h>

Fix the nm10300 build failure:

  In file included from arch/mn10300/kernel/csrc-mn10300.c:14:0:
  arch/mn10300/kernel/internal.h:42:1: error: unknown type name 'irqreturn_t'

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>