net/macb: only probe queues once and use stored values

When merging at91_ether and macb driver during 421d9df0 (net/macb: merge
at91_ether driver into macb driver) the probe function has been split. The code
dealing with initialization of queues is now moved in macb_init() which needs
information computed in the parent macb_probe() function.
So, add the queue_mask information to the private structure and use it when
needed in macb_init().

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>