drm/msm/dpu: remove ping pong split topology variables

removes left out variables of previous ping pong
split topology cleanup.

changes in v4:
	- none
changes in v5:
	- none

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>