media: atomisp-ov2680: Make ov2680_read_reg() support 24 bit registers

Some ov2680 registers like exposure are 24 bit,
ov2680_read_reg() already mostly supports this, we just
need to change the return type from u16 to u32.

Link: https://lore.kernel.org/linux-media/20211107171549.267583-8-hdegoede@redhat.com


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