stmmac: platform: fix default values of the filter bins setting

The commit 3b57de958e2a brought the support for a different amount of
the filter bins, but didn't update the platform driver that without
CONFIG_OF.

Fixes: 3b57de958e2a (net: stmmac: Support devicetree configs for mcast
and ucast filter entries)

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>