Make DataSourceFactory singletone

This is preparation for having a subclass of DataSourceFactory which
is only used in mediaserver process with OMA (forward-lock) use case.

Test: build
Bug: 142567168
Change-Id: I2a1ab3d1ae89f657a84376d9a95d4e814b545b4f
diff --git a/media/ndk/NdkMediaDataSource.cpp b/media/ndk/NdkMediaDataSource.cpp
index f6892e6..c1d4686 100644
--- a/media/ndk/NdkMediaDataSource.cpp
+++ b/media/ndk/NdkMediaDataSource.cpp
@@ -202,7 +202,7 @@
         headers.add(key8, value8);
     }
 
-    sp<DataSource> source = DataSourceFactory::CreateFromURI(service, uri, &headers);
+    sp<DataSource> source = DataSourceFactory::getInstance()->CreateFromURI(service, uri, &headers);
     if (source == NULL) {
         ALOGE("AMediaDataSource_newUri source is null");
         return NULL;