ar71xx/ath79: ew-dorin, fix the trigger level for WPS button

Because the WPS button had the wrong trigger level,
the failsafe mode was triggered quite often,
after this commit:
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=27f3f493de



Signed-off-by: Catrinel Catrinescu <cc@80211.de>