boot/barebox-aux: exclude git downloads from hash check

boot/barebox-aux: exclude git downloads from hash check

When barebox, and thus barebox-aux, are downloaded from a git tree, then
barebox-aux download fails because a hash check is attempted on the
downloaded archive:

    Could not fetch special ref 'v2020.03.0'; assuming it is not special.
    ERROR: No hash found for barebox-aux-v2020.03.0.tar.gz

This is because we only exclude from the check the archive of the bare
barebox:

    BR_NO_CHECK_HASH_FOR += $(BAREBOX_SOURCE)

However, the default name of an archive is based on the package name,
which for barebox-aux is not 'barebox'.

Since barebox-aux really uses the exact same source as the bare barebox,
it should also share the archive name.

This has two direct consequences and advantages:

  - the hash check is completely avoided for the barebox-aux archive;

  - the barebox-aux archive is not downloaded as it is already
    downloaded for barebox.

Reported-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>