mm/CRIS: clean up unused VALID_PAGE()

VALID_PAGE() has been removed from kernel long time ago, so clean up it.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>