media: Documentation: v42l_core: v4l2_ext_control

Describe p_area field from v4l2_ext_ctrl
Signed-off-by: Ricardo Ribalda Delgado <ribalda@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst

@@ -198,6 +198,11 @@ still cause this situation.
       - ``p_u32``
       - A pointer to a matrix control of unsigned 32-bit values. Valid if
 	this control is of type ``V4L2_CTRL_TYPE_U32``.
+    * -
+      - :c:type:`v4l2_area` *
+      - ``p_area``
+      - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
+        of type ``V4L2_CTRL_TYPE_AREA``.
     * -
       - void *
       - ``ptr``