media: atomisp: gc0310: Modernize and simply set_fmt(), get_fmt(), etc.

There only is 1 supported resolution allowing significant simplification
of the code; and also bring the code up2date with current subdev fmt
handling practices.

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>