qede: make driver reliable on unload after failures

In case recovery was not successful, netdev still should be
present. But we should clear cdev if something bad happens
on recovery.

We also check cdev for null on dev close. That could be a case
if recovery was not successful.

Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>