The generic GPIO would return 0 for low generic GPIO, and
something != 0 for high GPIO. Let's make this sane by clamping
the returned value to [0,1].
Reported-by: NEvgeny Boger <boger@contactless.ru>
Reviewed-by: NAlexandre Courbot <acourbot@nvidia.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>