pinctrl: bcm2835: 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. The bcm2835 pinctrl is also affected by this
warning.

Fix this by making the irqchip in the bcm2835 pinctrl driver immutable.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220614202831.236341-3-stefan.wahren@i2se.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>