Fix UB where multistats is written to over MAX_NIFO length, while it is only created with enabled_ifos length

The trigger stats are created based on the enabled ifo's of the pipeline:

https://git.ligo.org/lscsoft/spiir/-/blob/spiir-O4-EW-development/gstlal-spiir/gst/cuda/cohfar/background_stats_utils.c#L330

Whereas the memory accessed here is assumed to be based on MAX_NIFO's

https://git.ligo.org/lscsoft/spiir/-/blob/spiir-O4-EW-development/gstlal-spiir/gst/cuda/cohfar/cohfar_assignfar.c#L136

possibly related to #16