ionic: check qcq ptr in ionic_qcq_disable

There are a couple of error recovery paths that can come through
ionic_qcq_disable() without having set up the qcq, so we need
to make sure we have a valid qcq pointer before using it.

Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>