nvme/pci: Delete misleading queue-wrap comment

It is not theoretically possible for this driver to wrap twice while
processing completions. The driver allocates only 'queue_depth - 1'
tags, so there can never be more than that to reap when processing a
completion queue. Removing this misleading comment makes it a little
less likely people with broken controllers will blame the driver for
their spurious interrupts.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>