dt-bindings: backlight: lm3630a: Fix missing include

Example failed to compile due to undefined GPIO_ACTIVE_HIGH
fix that by adding the needed #include to the exammple.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml

@@ -93,6 +93,7 @@ additionalProperties: false
 
 examples:
   - |
+    #include <dt-bindings/gpio/gpio.h>
     i2c {
         #address-cells = <1>;
         #size-cells = <0>;