media: atomisp: Make bds_factors_list be type of struct u32_fract

The list contains the Bayer scale index, and rational fraction of it.
The struct u32_fract is suitable type to hold that. Convert the driver
to use latter instead of former.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>