block/nvme: Make nvme_identify() return boolean indicating error

Just for consistency, following the example documented since
commit e3fe3988 ("error: Document Error API usage rules"),
return a boolean value indicating an error is set or not.
Directly pass errp as the local_err is not requested in our
case.

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: 20201029093306.1063879-11-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>