Fixed broken '_GetDynamicFieldsDefinition' function.

Since $Self is passed via the method call ($Jobs{$Job}->{Module}->GetDynamicFieldsDefinition) you get the following error when passing $Self as a parameter:

 Message: Execute GetDynamicFieldsDefinition() of PostMaster::PreFilterModule Kernel::System::PostMaster::Filter::SystemMonitoring not successful with error Can't use string ("Kernel::System::PostMaster::Filt"...) as a HASH ref while "strict refs" in use at ./Kernel/System/PostMaster/Filter/SystemMonitoring.pm line 88.