msm: mdss: Call regulator enable/disable for both DSI controllers

There is ref count mismatch in number of enable/disable calls for
regulators with low power mode allowed flag which is resulting in
random system crashes. This change makes sure number of enable/disable
calls are same.

Change-Id: I0c1906df8c3a83e8740412c272179d3d9c514c0e
Signed-off-by: Rashi Bindra <rbindra@codeaurora.org>