Correct selection provider function signature for overriding

The function in the derived class did not override the function in the superclass
with the same name, only overloaded it. This caused that the selection in the
Data Manager tree view was not updated when the selection of the Data Manager
view part has been changed by another workbench part through the BlueBerry selection
service.

Signed-off-by: Miklos Espak <m.espak@ucl.ac.uk>