ostree: Commit to the branch with the updated naming

Use the board name instead of hardcoded 'generic' board, as done in
previous commits.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>
Reviewed-by: Denis Pynkin <denis.pynkin@collabora.com>
Reviewed-by: Luis Araujo <luis.araujo@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D7388