NVMe: Initialize device list head before starting

Driver recovery requires the device's list node to have been initialized.

Fixes: https://lkml.org/lkml/2015/3/22/262



Reported-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>