gpio: pwm: Fix return type of pwm_gpio_set

[juergh]

Fixes the following build failure:

drivers/gpio/gpio-pwm.c:108:26: error: assignment to 'int (*)(struct gpio_chip , unsigned int, int)' from incompatible pointer type 'void ()(struct gpio_chip *, unsigned int, int)' [-Wincompatible-pointer-types]
108 | pwm_gpio->gc.set = pwm_gpio_set;
| ^
drivers/gpio/gpio-pwm.c:30:13: note: 'pwm_gpio_set' declared here
30 | static void pwm_gpio_set(struct gpio_chip *gc, unsigned int off, int val)
| ^~~~~~~~~~~~

Fixes: 8b95d76 ("drivers/gpio: Add a driver that wraps the PWM API as a GPIO controller")

[juergh]

This is required for kernels >=6.17 due to d9d87d9.

[popcornmix]

Ah:

$ grep CONFIG_GPIO_PWM  .config
# CONFIG_GPIO_PWM is not set

looks like we don't have this enabled, so don't see the error.
But it looks fine to me.

[pelwell]

rpi-6.18.y would have been a more logical target branch, but I'll backport it.

[6by9]

TBH I'd be tempted to remove the driver totally.

I'd written it so that you could use some outputs of a NXP PCA9685 16 chan PWM controller as GPIOs , but the driver for that chip can now do that natively. (It looks like it's been able to do that for 10 years, so I'm not sure why I thought it was necessary in 2021).