Pass the correct number of displays based on HWC version

Change-Id: I27372f5d3102ad56f6d67722d631ae18d37f8330
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index ac2257e..8080d3b 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -58,9 +58,7 @@
     };
 
     enum {
-        MAIN = 0,
-        HDMI = 1,
-        MAX_DISPLAYS
+        MAX_DISPLAYS = HWC_NUM_DISPLAY_TYPES + 1
     };
 
     HWComposer(
@@ -245,6 +243,7 @@
     // TODO: decide whether mLists[i>0] should be non-NULL when display i is
     //       not attached/enabled.
     struct hwc_display_contents_1*  mLists[MAX_DISPLAYS];
+    size_t                          mNumDisplays;
 
     size_t                          mCapacity;
     mutable size_t                  mNumOVLayers;