media: doc: Replace symbol for V4L2_CTRL_TYPE_H264_PRED_WEIGHTS

When V4L2_CTRL_TYPE_H264_PRED_WEIGHTS was added, adding a replace
symbol directive in videodev2.h.rst.exceptions was missed.

Now that the control type is destaged, it's important to fix this.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>