Fix erroneous comment in LALSimIMRNRWaveforms.c

Description

Correct error in comment -- no functional changes at all.

API Changes and Justification

Backwards Compatible Changes

• This change introduces no API changes
• This change adds new API calls

Backwards Incompatible Changes

• This change modifies an existing API
• This change removes an existing API

Review Status

Just correcting a comment -- no functional changes at all.