block/nvme: Simplify nvme_cmd_sync()

As all commands use the ADMIN queue, it is pointless to pass
it as argument each time. Remove the argument, and rename the
function as nvme_admin_cmd_sync() to make this new behavior
clearer.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20201029093306.1063879-17-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>