nvme: use vendor it from identify

Use the vendor ID from the identify data instead of the PCI device to
make the SCSI translation layer independent from the PCI driver.  The NVMe
spec defines them as having the same value for current PCIe devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>