stmmac: correct mc_filter local variable in set_filter and set_mac_addr call

Testing revealed that the local variable mc_filter was dimensioned
incorrectly for all possible configurations and get_mac_addr should
have been set_mac_addr (a typo). Make sure mc_filter is dimensioned
to 8 32-bit unsigned longs - the largest size of the Synopsys
multicast filter register set.

Signed-off-by: Vince Bridgers <vbridger@opensource.altera.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>