[amarok] src: Fix DynamicModel test

[Matěj Laitl]

On 12. 7. 2012 Matěj Laitl wrote:
> Again, place for hard-to-find bugs in future. You should 
> Amarok::Compontents::setEngineController( new EngineControllerMock() ) in 
> test's initTestCase() instead.

And when https://git.reviewboard.kde.org/r/105524/ is merged, you even can use 
plain vanilla EngineController directly, see 
https://git.reviewboard.kde.org/r/105524/diff/#9.6

	Matěj