msm: mdss: Fix mdp3 core clock calculation with scaling

Because scale factor was initialized as 0 mdp3 core clock were computed as zero
when blending was not enabled. Fix issue by initializing scale factor properly.

Change-Id: I3bc6edb7c8a61d8d39921177b283202835e32991
Signed-off-by: Sachin Bhayare <sachin.bhayare@codeaurora.org>