Fix the doc so it uses the defined parameter names for the signals

The documentation needs to use the defined parameter names for the signals
as this is what QML will make them available as if they are used in a
connection to that signal.

Task-number: QTBUG-35694
Change-Id: I0f56b9e1ace45cfff72c45273dd64766e3c792f2
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>