kernel/3.1x: yaffs: fix handling of small-page NAND devices

Since the yaffs code update (r39084), it is not
possible to install OpenWrt on RouterBoards with
small-page NAND chips. Fix the yaffs code to make
it work again.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39409 3c298f89-4303-0410-b956-a3cf2f4a3e73