drm: msm: sde: clear opmode with ltm init disable

Continuous on and off of ltm feature with partial update
can lead to ppdone timeout's if the ltm feature is
not disable with ltm init disable. Hence Clear the
ltm opmode configuaration in ltm init disable instead
of a disable mask.

Change-Id: If09ae78807c21c0dee1bd4f29c88a1e9499a9917
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>