media: drivers/index.rst: add missing rkisp1 entry

The Documentation/driver-api/media/drivers/rkisp1.rst file
wasn't referenced in the index.rst file, so it was never included.

Add it.
Signed-off-by: NHans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/media/drivers/index.rst

@@ -21,6 +21,7 @@ Video4Linux (V4L) drivers
 	pvrusb2
 	pxa_camera
 	radiotrack
+	rkisp1
 	saa7134-devel
 	sh_mobile_ceu_camera
 	tuners