nvmet-fcloop: swap the list_add_tail arguments

The first argument of list_add_tail function is the new element which
should be added to the list which is the second argument. Swap the
arguments to allow processing more than one element at a time.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>