webadmin: Fixed event listener assignment (Findbugs)

Assign a newly-created listener to the right listener member. This is
a response to findbugs warning UWF_UNWRITTEN_FIELD.

Change-Id: I35bb5fb094168e44bd77f4847067aa94b7c1fe22
Signed-off-by: Lior Vernia <lvernia@redhat.com>