media: atomisp: Rename video_out_preview to video_out

Now that we have only 1 /dev/video# node for output for all different
run-modes (with only 1 run-mode at a time) using video_out_preview for
the remaining atomisp_pipe does not properly reflect that this is
*the* output pipe. Fo the following renames to fix the naming:

s/video_out_preview/video_out/
s/ATOMISP_SUBDEV_PAD_SOURCE_PREVIEW/ATOMISP_SUBDEV_PAD_SOURCE/

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>