net: bcmgenet: Ensure all TX/RX queues DMAs are disabled

Make sure that we disable each of the TX and RX queues in the TDMA and
RDMA control registers. This is a correctness change to be symmetrical
with the code that enables the TX and RX queues.

Tested-by: Maxime Ripard <maxime@cerno.tech>
Fixes: 1c1008c7

 ("net: bcmgenet: add main driver file")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>