fsi: master-ast-cf: Add MODULE_FIRMWARE macro

The module loads firmware so add a MODULE_FIRMWARE macro to provide that
information via modinfo.

Fixes: 6a794a27

 ("fsi: master-ast-cf: Add new FSI master using Aspeed ColdFire")
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Link: https://lore.kernel.org/r/20230628095039.26218-1-juerg.haefliger@canonical.com
Signed-off-by: Joel Stanley <joel@jms.id.au>