pinctrl: bcm2835: Fix permissions of persist_gpio_outputs

The commit 8ff05989 ("pinctrl: bcm2835: Make pin freeing behavior
configurable") unintentionally made the module parameter
persist_gpio_outputs changeable at runtime. So drop the write permission
in order to make the freeing behavior predictable for user applications.

Fixes: 8ff05989 ("pinctrl: bcm2835: Make pin freeing behavior configurable")
Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Closes: https://lore.kernel.org/linux-gpio/Zjk-C0nLmlynqLAE@surfacebook.localdomain/Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20240603181938.76047-2-wahrenst@gmx.netSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/bcm/pinctrl-bcm2835.c

@@ -245,7 +245,7 @@ static const char * const irq_type_names[] = {
 };
 
 static bool persist_gpio_outputs;
-module_param(persist_gpio_outputs, bool, 0644);
+module_param(persist_gpio_outputs, bool, 0444);
 MODULE_PARM_DESC(persist_gpio_outputs, "Enable GPIO_OUT persistence when pin is freed");
 
 static inline u32 bcm2835_gpio_rd(struct bcm2835_pinctrl *pc, unsigned reg)