ar71xx: oolite: the buttons are not active_low

this caused factory resets when reboot was pressed

Signed-off-by: Brent Thomson <brentthomson@gmail.com>
Signed-off-by: John Crispin <blogic@openwrt.org>

Backport of r41932

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@41972 3c298f89-4303-0410-b956-a3cf2f4a3e73