drm/amd/display: Add missing dml2 init value for dcn35

[Why]
For lighting up, some dml2 params needs to be initialized.
One of them escaped initial patch under:
"drm/amd/display: Add DCN35 DML2 support"

[How]
Add missing initialization.

Fixes: 115009d1

 ("drm/amd/display: Add DCN35 DML2 support")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Hersen Wu <hersenxs.wu@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>