media: dt-bindings: adv7604: Fix documentation for hpd-gpios

As of [1] the hpd-gpios property is optional, document it as such.

1. commit 269bd132 ("[media] media: adv7604: improve usage of gpiod API")
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/devicetree/bindings/media/i2c/adv7604.txt

@@ -19,10 +19,6 @@ Required Properties:
     slave device on the I2C bus. The main address is mandatory, others are
     optional and revert to defaults if not specified.
 
-  - hpd-gpios: References to the GPIOs that control the HDMI hot-plug
-    detection pins, one per HDMI input. The active flag indicates the GPIO
-    level that enables hot-plug detection.
-
 The device node must contain one 'port' child node per device input and output
 port, in accordance with the video interface bindings defined in
 Documentation/devicetree/bindings/media/video-interfaces.txt. The port nodes
@@ -37,6 +33,9 @@ The digital output port node must contain at least one endpoint.
 
 Optional Properties:
 
+  - hpd-gpios: References to the GPIOs that control the HDMI hot-plug
+    detection pins, one per HDMI input. The active flag indicates the GPIO
+    level that enables hot-plug detection.
   - reset-gpios: Reference to the GPIO connected to the device's reset pin.
   - default-input: Select which input is selected after reset.
   - reg-names : Names of maps with programmable addresses.