iscsi-target: Fix CmdSN comparison (use cmd->cmd_sn instead of cmd->stat_sn)

Commit 64c13330a389 ("iscsi-target: Fix bug in handling of ExpStatSN
ACK during u32 wrap-around") introduced a bug where we compare the
wrong SN against our ExpCmdSN.

Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_erl2.c

@@ -372,7 +372,7 @@ int iscsit_prepare_cmds_for_realligance(struct iscsi_conn *conn)
 		 * made generic here.
 		 */
 		if (!(cmd->cmd_flags & ICF_OOO_CMDSN) && !cmd->immediate_cmd &&
-		     iscsi_sna_gte(cmd->stat_sn, conn->sess->exp_cmd_sn)) {
+		     iscsi_sna_gte(cmd->cmd_sn, conn->sess->exp_cmd_sn)) {
 			list_del(&cmd->i_conn_node);
 			spin_unlock_bh(&conn->cmd_lock);
 			iscsit_free_cmd(cmd);