msm: mdss: send correct bpp value for BW calc

After bootup the BW vote is higher due to wrong bpp
value used for calculation. Due to higher bpp value,
BW voting is very high before first suspend.

Change-Id: I4e7bc33bcdbab7708127bed09895af149971253e
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>