drm/amd/display: Revert Avoid overflow assignment

This reverts commit a1526878 ("drm/amd/display: Avoid overflow assignment in link_dp_cts")
Due to regression causing DPMS hang.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Gabe Teeger <Gabe.Teeger@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>