net: qede: fix use-after-free on recovery and AER handling

Set edev->cdev pointer to NULL after calling remove() callback to avoid
using of already freed object.

Fixes: ccc67ef5

 ("qede: Error recovery process")
Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>