media: media/test_drivers: Replace open-coded parity calculation with parity8()
Refactor parity calculations to use the standard parity8() helper.
This change eliminates redundant implementations.
Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>