pinctrl: sunxi: drop lock on error path

I forgot to drop the lock for the return inside the loop
protected by the spinlock in the pin config routine when
merging in -rc7 in commit 6ad30ce0

Reported-by: Sherman Yin <syin@broadcom.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>