Use NULL not 0 for raw pointers

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

Change-Id: Iaec3413a59ccbf233c98fcd918cc7d70ac5da9fa
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 98abfbd..02c85cd 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -148,8 +148,8 @@
                                     int channelMask      = 0,
                                     int frameCount       = 0,
                                     uint32_t flags       = 0,
-                                    callback_t cbf       = 0,
-                                    void* user           = 0,
+                                    callback_t cbf       = NULL,
+                                    void* user           = NULL,
                                     int notificationFrames = 0,
                                     int sessionId = 0);
 
@@ -180,8 +180,8 @@
                                     int channelMask     = 0,
                                     const sp<IMemory>& sharedBuffer = 0,
                                     uint32_t flags      = 0,
-                                    callback_t cbf      = 0,
-                                    void* user          = 0,
+                                    callback_t cbf      = NULL,
+                                    void* user          = NULL,
                                     int notificationFrames = 0,
                                     int sessionId = 0);
 
@@ -204,8 +204,8 @@
                             int channelMask     = 0,
                             int frameCount      = 0,
                             uint32_t flags      = 0,
-                            callback_t cbf      = 0,
-                            void* user          = 0,
+                            callback_t cbf      = NULL,
+                            void* user          = NULL,
                             int notificationFrames = 0,
                             const sp<IMemory>& sharedBuffer = 0,
                             bool threadCanCallJava = false,