video:msm: Fix histogram error check logic

Current error check logic is incorrect. Starting the histogram should
throw an error if the histogram current state (mdp_is_hist_data) is
already true.

Similarly, stopping the histogram should only throw an error if the
histogram current state has already been set to false.

In the cases of suspend/resume the mdp_histogram_ctrl calls should only be
allowed when the histogram desired state (mdp_is_hist_start) is true.

Change-Id: Idef307293a7e4fb70807e9cea53078bf3cc67f15
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>