block/nvme: Set request_alignment at initialization

Commit bdd6a90a ("block: Add VFIO based NVMe driver")
sets the request_alignment in nvme_refresh_limits().
For consistency, also set it during initialization.

Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20201029093306.1063879-18-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>