Update Element.isCompatible() to work with NONE.

In the past, we used a null reference to signify a user-created Element. The
use of DataType.NONE for user-created Elements thus required an update to our
Element compatibility check.

Change-Id: I3293a645eff85c9040487c22f3a3240862f74350
diff --git a/graphics/java/android/renderscript/Element.java b/graphics/java/android/renderscript/Element.java
index f6a0281..2c0925b 100644
--- a/graphics/java/android/renderscript/Element.java
+++ b/graphics/java/android/renderscript/Element.java
@@ -933,10 +933,10 @@
 
         // Ignore mKind because it is allowed to be different (user vs. pixel).
         // We also ignore mNormalized because it can be different. The mType
-        // field must be non-null since we require name equivalence for
-        // user-created Elements.
+        // field must not be NONE since we require name equivalence for
+        // all user-created Elements.
         return ((mSize == e.mSize) &&
-                (mType != null) &&
+                (mType != DataType.NONE) &&
                 (mType == e.mType) &&
                 (mVectorSize == e.mVectorSize));
     }