drm/msm/dsi: Drop VDD regulator for MSM8916

VDD regulator input was specified for MSM8916. It turns our that this
regulator is used for the display panels used on MSM8916 platforms, but
not the DSI controller itself. Drop this regulator from the list.

Reported-by: Vinay Simha <vinaysimha@inforcecomputing.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>