src() called as a getter should return the video src

It can be handy that src() returns the player object when it is invoked but it does not match the behavior of the corresponding property on the video element. Ignoring the spec however, while the video element is running the resource selection algorithm, currentSrc may be undefined. If the video source has been specified through an attribute on the video element, src() is the natural way to expose that URL programmatically. Without this change, it's necessary to bypass the player and interact with the tech directly to determine the value of the src attribute.