net/mlx5e: Avoid NULL pointer access in case of configuration failure

In case a configuration operation that involves closing and re-opening
resources (e.g RX/TX queue size change) fails at the re-opening stage
these resources will remain closed.
So when executing (following) configuration operations (e.g ifconfig
down) we cannot assume that these resources are available.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>