dt-bindings: pinctrl: stm32: Fix missing 'clocks' property in examples

Now that examples are validated against the DT schema, an error with
required 'clocks' property missing is exposed:

Documentation/devicetree/bindings/pinctrl/st,stm32-pinctrl.example.dt.yaml: \
pinctrl@40020000: gpio@0: 'clocks' is a required property
Documentation/devicetree/bindings/pinctrl/st,stm32-pinctrl.example.dt.yaml: \
pinctrl@50020000: gpio@1000: 'clocks' is a required property
Documentation/devicetree/bindings/pinctrl/st,stm32-pinctrl.example.dt.yaml: \
pinctrl@50020000: gpio@2000: 'clocks' is a required property

Add the missing 'clocks' properties to the examples to fix the errors.

Fixes: 2c9239c125f0 ("dt-bindings: pinctrl: Convert stm32 pinctrl bindings to json-schema")
Cc: Linus Walleij <[e-mail]>
Cc: Maxime Coquelin <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Acked-by: Alexandre TORGUE <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/pinctrl/st,stm32-pinctrl.yaml

···
 examples:
   - |
     #include <dt-bindings/pinctrl/stm32-pinfunc.h>
+    #include <dt-bindings/mfd/stm32f4-rcc.h>
     //Example 1
       pinctrl@40020000 {
               #address-cells = <1>;
···
                       #gpio-cells = <2>;
                       reg = <0x0 0x400>;
                       resets = <&reset_ahb1 0>;
+                      clocks = <&rcc 0 STM32F4_AHB1_CLOCK(GPIOA)>;
                       st,bank-name = "GPIOA";
               };
        };
···
                       #gpio-cells = <2>;
                       reg = <0x1000 0x400>;
                       resets = <&reset_ahb1 0>;
+                      clocks = <&rcc 0 STM32F4_AHB1_CLOCK(GPIOB)>;
                       st,bank-name = "GPIOB";
                       gpio-ranges = <&pinctrl 0 0 16>;
               };
···
                       #gpio-cells = <2>;
                       reg = <0x2000 0x400>;
                       resets = <&reset_ahb1 0>;
+                      clocks = <&rcc 0 STM32F4_AHB1_CLOCK(GPIOC)>;
                       st,bank-name = "GPIOC";
                       ngpios = <5>;
                       gpio-ranges = <&pinctrl 0 16 3>,