block/nvme: Replace magic value by SCALE_MS definition

Use self-explicit SCALE_MS definition instead of magic value
(missed in similar commit e4f310fe).

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200922083821.578519-7-philmd@redhat.com>