Wrong variable used

[pulkitgoyal56]

https://github.com/pulkitgoyal56/fNIRS-attentional-load/blob/e9e9faa8b4d123553f707b390c8da27afdf1502c/nirs.py#L954
https://github.com/pulkitgoyal56/fNIRS-attentional-load/blob/e9e9faa8b4d123553f707b390c8da27afdf1502c/nirs.py#L956

TODO: Change ax to axs