drm/amd/display: set MSA vsp/hsp to 0 for positive polarity for DP 128b/132b

[why]
There is a bug in MSA programming sequence that mistakenly set
MSA vsp/hsp to 1 for positive polarity. This is incorrect.

Reviewed-by: Ariel Bernstein <Eric.Bernstein@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>