net: calxedaxgmac: fix clearing of old filter addresses

In commit 2ee68f62 (net: calxedaxgmac: fix various errors in
xgmac_set_rx_mode), a fix to clean-up old address entries was added.
However, the loop to zero out the entries failed to increment the register
address resulting in only 1 entry getting cleared. Fix this to correctly
use the loop index. Also, the end of the loop condition was off by 1 and
should have been <= rather than <.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: David S. Miller <davem@davemloft.net>