pinctrl: mediatek: mt7622: align error handling of mtk_hw_get_value call

Make consistent error handling of all mtk_hw_get_value occurrences using
propagating error code from the internal instead of creating a new one.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>