xfs/078: disable all concurrency scaling

Disable concurrency scaling to avoid mismatching output on systems with
a large CPU count.

Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>