drm/msm/dsi-staging: remove post delay after sending roi commands

Change removes delay after sending 2A/2B partial update commands.
This delay is causing framedrop for next frame when we miss
kickoff window.

CRs-Fixed: 2179648
Change-Id: I1fe84f7d2d0e8bf3d81a14dd56b8756ba6598fe9
Signed-off-by: Vara Reddy <varar@codeaurora.org>