pinctrl: stm32: fix bad location of gpiochip_lock_as_irq

Move gpio lock as irq from "domain alloc" callback to "domain activate"
callback. It will allow to use gpiolib sysfs correctly.

Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>