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

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

commit 64fe4f4f181cc2fe97d4176bf6ee6e3725ae33ec upstream.

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>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>