NVMe: Use pci_stop_and_remove_bus_device_locked()

Race conditions are theoretically possible between the NVMe PCI device
removal and the generic PCI bus rescan and device removal that can be
triggered via sysfs.

To avoid those race conditions make the NVMe code use
pci_stop_and_remove_bus_device_locked().

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>