gpio: revert get() to non-errorprogating behaviour

commit e20538b8
("gpio: Propagate errors from chip->get()")
started to propagate errors from the .get() functions since
we can get errors from the infrastructure of e.g. slowbus
GPIO expanders.

However it turns out a bunch of drivers relied on the core
to clamp the value, so we need to revert to the old behaviour
and go over all drivers and fix them to conform to the
expectations of the core before we go back to propagating
the error code.

Cc: stable@vger.kernel.org # 4.3+
Cc: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Fixes: e20538b8

 ("gpio: Propagate errors from chip->get()")
Reported-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>