mn10300: mm/dma-alloc.c needs <linux/export.h>

Fix the warnings:

  arch/mn10300/mm/dma-alloc.c: At top level:
  arch/mn10300/mm/dma-alloc.c:63:1: warning: data definition has no type or storage class [enabled by default]
  arch/mn10300/mm/dma-alloc.c:63:1: warning: type defaults to 'int' in declaration of 'EXPORT_SYMBOL' [-Wimplicit-int]
  arch/mn10300/mm/dma-alloc.c:63:1: warning: parameter names (without types) in function declaration [enabled by default]
  arch/mn10300/mm/dma-alloc.c:75:1: warning: data definition has no type or storage class [enabled by default]
  arch/mn10300/mm/dma-alloc.c:75:1: warning: type defaults to 'int' in declaration of 'EXPORT_SYMBOL' [-Wimplicit-int]
  arch/mn10300/mm/dma-alloc.c:75:1: warning: parameter names (without types) in function declaration [enabled by default]

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>