pinctrl: qcom: spmi-gpio: Mark expected switch fall-through

When fall-through warnings was enabled by default the following warnings
was starting to show up:

../drivers/pinctrl/qcom/pinctrl-spmi-gpio.c: In function ‘pmic_gpio_populate’:
../drivers/pinctrl/qcom/pinctrl-spmi-gpio.c:815:20: warning: this statement may fall
through [-Wimplicit-fallthrough=]
pad->have_buffer = true;
~~~~~~~~~~~~~~~~~^~~~~~
../drivers/pinctrl/qcom/pinctrl-spmi-gpio.c:816:2: note: here
case PMIC_GPIO_SUBTYPE_GPIOC_4CH:
^~~~
../drivers/pinctrl/qcom/pinctrl-spmi-gpio.c:820:20: warning: this statement may fall
through [-Wimplicit-fallthrough=]
pad->have_buffer = true;
~~~~~~~~~~~~~~~~~^~~~~~
../drivers/pinctrl/qcom/pinctrl-spmi-gpio.c:821:2: note: here
case PMIC_GPIO_SUBTYPE_GPIOC_8CH:
^~~~

Rework so that the compiler doesn't warn about fall-through.

Fixes: d93512ef0f0e ("Makefile: Globally enable fall-through warning")
Signed-off-by: Anders Roxell <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/qcom/pinctrl-spmi-gpio.c

···
 	switch (subtype) {
 	case PMIC_GPIO_SUBTYPE_GPIO_4CH:
 		pad->have_buffer = true;
+		/* Fall through */
 	case PMIC_GPIO_SUBTYPE_GPIOC_4CH:
 		pad->num_sources = 4;
 		break;
 	case PMIC_GPIO_SUBTYPE_GPIO_8CH:
 		pad->have_buffer = true;
+		/* Fall through */
 	case PMIC_GPIO_SUBTYPE_GPIOC_8CH:
 		pad->num_sources = 8;
 		break;