media: atomisp: Remove unused mipi_frame_size field from atomisp_[sub_]device

Both the atomisp_device and the atomisp_sub_device structs have
an unused mipi_frame_size field, remove the field from both.

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>