display: Fix warnings, make warnings as errors

Change-Id: I61f22765b04112be48e62135db930c415c9c7d37
diff --git a/libgralloc/alloc_controller.cpp b/libgralloc/alloc_controller.cpp
index 2ba0d6a..97255ba 100644
--- a/libgralloc/alloc_controller.cpp
+++ b/libgralloc/alloc_controller.cpp
@@ -152,7 +152,7 @@
 
 IMemAlloc* IonController::getAllocator(int flags)
 {
-    IMemAlloc* memalloc;
+    IMemAlloc* memalloc = NULL;
     if (flags & private_handle_t::PRIV_FLAGS_USES_ION) {
         memalloc = mIonAlloc;
     } else {