enable_subchannel() is already done during is_dev_possibly_bootable()
(which is called from find_boot_device() -> find_subch()), so there
is no need to do this again in the main() function.

Message-Id: <20200806105349.632-9-thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>