Use NULL not 0 for raw pointers

Use if (p != NULL) instead of if (ptr)

Change-Id: Iaec3413a59ccbf233c98fcd918cc7d70ac5da9fa
diff --git a/media/libmedia/IAudioFlinger.cpp b/media/libmedia/IAudioFlinger.cpp
index 0d442ef..7c5589d 100644
--- a/media/libmedia/IAudioFlinger.cpp
+++ b/media/libmedia/IAudioFlinger.cpp
@@ -640,7 +640,7 @@
                 *id = tmp;
             }
             tmp = reply.readInt32();
-            if (enabled) {
+            if (enabled != NULL) {
                 *enabled = tmp;
             }
             effect = interface_cast<IEffect>(reply.readStrongBinder());