ar71xx: ar934x-nfc: disable subpage write when hardware ECC is used

It is not supported by the controller.

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38234 3c298f89-4303-0410-b956-a3cf2f4a3e73