drm/msm/dsi-staging: Set transfer time to zero as per mode of timing node

Currently, mdp_transfer_time_us is being set to zero for video
mode panels. This leads to zero mdp_transfer_time_us for command
mode in case of video mode panels supporting panel operating
mode switch. As a  result, there is miscalculation of clock to
zero when command mode doesn't support dynamic clock switch. This
change sets the mdp_transfer_time_us to zero for video modes.

Change-Id: I6e798125921db9ea2d76b76853a28cd981747617
Signed-off-by: Lipsa Rout <lrout@codeaurora.org>