media: atomisp: Remove unused fields from struct atomisp_input_subdev

Remove unused fields from struct atomisp_input_subdev:

1. frame_size is never used at all
2. sensor_index is always 0, just directly pass 0 in the single user.

Link: https://lore.kernel.org/r/20230518153733.195306-3-hdegoede@redhat.com



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>