drm/amd/display: Use max target bpp override option

[Why]
Max target bpp override is an option for working around
DSC issues. It is supported on DC level, but was not
used in DM.

[How]
Use actual option value instead of 0.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>