Bug#915737: open-ath9k-htc-firmware still uses GCC 7

[Matthias Klose]

Package: src:open-ath9k-htc-firmware
Version: 1.4.0-97-g75b3e59+dfsg-1
Severity: serious
Tags: sid buster

Please use the default GCC for the package so that we can remove GCC 7 for the
buster release.