Return error for XLALSimIMRSEOBNRv4HMROM_Modes

Description

When using XLALSimIMRSEOBNRv4HMROM_Modes the functions always returns XLAL_SUCCESS even when the generation of the modes failed. This is somehow inconvenient when you check for errors by reading the returned value of the function. I just return the variable retcode that was already computed and stores the result of the evaluation of the internal function.

This is an auxiliary function that is not used for PE.

@roberto.cotesta @michael.puerrer @maria.haney

API Changes and Justification

Backwards Compatible Changes

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Backwards Incompatible Changes

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Review Status

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