hwc: mdpcomp: Use actual usable mixer stages from driver

The driver now sends the actual usable mixer stages, so no need to
deduct the STAGE_UNUSED and STAGE_BASE.

Change-Id: I3690d10b5ccf83cab499871479768fcd5cdb2a4e
diff --git a/libqdutils/mdp_version.cpp b/libqdutils/mdp_version.cpp
index f8729a5..8ca0824 100644
--- a/libqdutils/mdp_version.cpp
+++ b/libqdutils/mdp_version.cpp
@@ -101,7 +101,7 @@
     mSourceSplitAlways = false;
     mRGBHasNoScalar = false;
     mRotDownscale = false;
-    mBlendStages = 6; //min no. of stages supported by MDP.
+    mBlendStages = 4; //min no. of stages supported by MDP.
 
     // this is the default limit of mixer unless driver reports it.
     // For resolutions beyond this, we use dual/split overlay pipes.