media: atomisp-ov2680: Remove the ov2680_res and N_RES global variables

The ov2680_res and N_RES global variables are just hardcoded as aliases
for ov2680_res_preview and N_RES_PREVIEW, remove them.

Link: https://lore.kernel.org/linux-media/20211107171549.267583-5-hdegoede@redhat.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>