Fix gdbus-codegen command-line interface

[Denton-L]

Previously, running cmake . && make would result in the following error:

usage: gdbus-codegen [-h] [--interface-prefix PREFIX]
                     [--c-namespace NAMESPACE] [--c-generate-object-manager]
                     [--c-generate-autocleanup {none,objects,all}]
                     [--generate-docbook OUTFILES] [--pragma-once]
                     [--annotate WHAT KEY VALUE WHAT KEY VALUE WHAT KEY VALUE]
                     [--generate-c-code OUTFILES | --header | --body | --interface-info-header | --interface-info-body]
                     [--output FILE | --output-directory OUTDIR]
                     [FILE [FILE ...]]
gdbus-codegen: error: ambiguous option: --interface could match --interface-prefix, --interface-info-header, --interface-info-body

This patch fixes that so it is no longer ambiguous.

[f1u77y]

Thanks!