nvme-auth: update sc_c in host response

The sc_c field is currently not updated in the host response to the
controller challenge leading to failures while attempting secure
channel concatenation. Fix this by adding a new sc_c variable to the
dhchap queue context structure which is appropriately set during
negotiate and then used in the host response.

Fixes: e88a7595 ("nvme-tcp: request secure channel concatenation")
Signed-off-by: Martin George <marting@netapp.com>
Signed-off-by: Prashanth Adurthi <prashana@netapp.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>