r6040: fix check against MCRO_HASHEN bit in r6040_multicast_list

We are checking whether the MCR0_HASHEN bit is set using a logical and
instead of bitwise and, fix that.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>