drm/amd/display: Do not bypass chroma scaling in 1:1 case

[Why]
When doing 2:1 downscaling on a YUV sub-sampled format, the chroma
scaling ratio is 1:1. Since chroma has cositing, it is needed to do
scaling on the chroma plane(s) and not to bypass chroma scaling.

[How]
Do not set the chroma taps to one when the chroma ratio is identity
and the input format is a sub-sampled YUV format.

Reviewed-by: Samson Tam <samson.tam@amd.com>
Signed-off-by: Navid Assadian <Navid.Assadian@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>