pinctrl: mt7622: fix error path on failing at groups building

It should be to return an error code when failing at groups building.

Cc: stable@vger.kernel.org
Fixes: d6ed9355 ("pinctrl: mediatek: add pinctrl driver for MT7622 SoC")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>