net: qede: stop adding events on an already destroyed workqueue

net: qede: stop adding events on an already destroyed workqueue

[ Upstream commit 4079c7f7a2a00ab403c177ce723b560de59139c3 ]

Set rdma_wq pointer to NULL after destroying the workqueue and check
for it when adding new events to fix crashes on driver unload.

Fixes: cee9fbd8e2e9 ("qede: Add qedr framework")
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>