Use the setDataSource(String) overload for non assets/file paths

The setDataSource(Context, Uri) is used for passing a Uri that refers
to data in a content provider. Whereas the path passed here is going to
be http/rtsp instead. This fixes the warning that comes up about it not
being able to open the path provided.

Task-number: QTBUG-50539
Change-Id: I79882fb6d6a5683b6b95f8f9d4e2af86ea916831
Reviewed-by: VaL Doroshchuk <valentyn.doroshchuk@qt.io>