While trying to simplify the code using a macro, we forgot
the 12-bit shift... Correct that.

Fixes: fad1eb68 ("block/nvme: Use register definitions from 'block/nvme.h'")
Reported-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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>
Message-id: 20201029093306.1063879-19-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>