drm/amd/display: Fix ref_count messed up issue

In the full update type, need to add ref_count to the newly
created dc_state->stream. It made mistake to add ref_count to
dc->current_state->stream which keeps adding up without release.

Signed-off-by: Jerry Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>