nvme: Free ctrl device name on init failure

Free the kobject name that was allocated for the controller device on
failure rather than its parent.

Fixes: d22524a4 ("nvme: switch controller refcounting to use struct device")
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>