drm/msm/dp: update stream on sequence in mst mode

Moving ctrl state to SEND_VIDEO before stream ch allocation
causes the controller to enter into bad state in mst mode.
This change corrects the programming sequence as per the hw
recommendation.

CRs-Fixed: 2280286
Change-Id: I249bbc3403c137df58b6bbbec80eb554422c6351
Signed-off-by: Govinda Rajulu Chenna <gchenna@codeaurora.org>