I think you have to add
xmlns:ns="http://www.w3.org/1999/xlink" to the <svg> tag, and then use
ns:href in the <a> tag. See
here.
The first piece defines the "ns" namespace, where "ns" is just an arbitrary name, you can choose whatever name you like. When you use "ns:href", it means the "href" attribute from the "http://www.w3.org/1999/xlink" (that we have defined as "ns") specification.