iscsi-target: Fix memory corruption in iscsit_logout_post_handler_diffcid

iscsi-target: Fix memory corruption in iscsit_logout_post_handler_diffcid

This patch fixes a bug in iscsit_logout_post_handler_diffcid() where
a pointer used as storage for list_for_each_entry() was incorrectly
being used to determine if no matching entry had been found.

This patch changes iscsit_logout_post_handler_diffcid() to key off
bool conn_found to determine if the function needs to exit early.

Reported-by: Joern Engel <[email protected]>
Cc: <[email protected]> # v3.1+
Signed-off-by: Nicholas Bellinger <[email protected]>