drm/amd/display: Don't set DSC for phantom pipes

[Description]
Don't set DSC bit for phantom pipes, not
required since phantom pipe don't have
any actual output

Reviewed-by: Jun Lei <[e-mail]>
Acked-by: Brian Chang <[e-mail]>
Signed-off-by: Alvin Lee <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dml/dcn32/dcn32_fpu.c

···
 						phantom_stream->timing.v_front_porch +
 						phantom_stream->timing.v_sync_width +
 						phantom_bp;
+	phantom_stream->timing.flags.DSC = 0; // Don't need DSC for phantom timing
 }
 
 /**