media: atomisp: gc0310: Replace custom reg access functions with smbus helpers

The gc0310 uses 8 bit register addresses which makes it compatible
with the standard smbus access functions.

Drop the custom reg access helpers, replacing them with the smbus
access functions.

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>