pinctrl: qcom: spmi-gpio: make the irqchip immutable

Commit 6c846d02

 ("gpio: Don't fiddle with irqchips marked as
immutable") added a warning to indicate if the gpiolib is altering the
internals of irqchips.

Following this change the following warning is now observed for the SPMI
PMIC pinctrl driver:
gpio gpiochip1: (200f000.spmi:pmic@0:gpio@c000): not an immutable chip, please consider fixing it!

Fix this by making the irqchip in the SPMI PMIC pinctrl driver immutable.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20220624195112.894916-1-robimarko@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>