display: Fix build with current msm mdp kernel header

Commit 999ee56abce2a0f25b3d4518a8a225fe74b3aae5 introduced a helper macro
to calculate the actual mdp revision. Use this here.

Change-Id: Ied0e0e32a4ce41acd367b81a3710c0b25559741d
Merge "display: Fix build with current msm mdp kernel header" into du44