stmmac: fix autoneg in set_pauseparam

This patch fixes a bug in the set_pauseparam
function that didn't well manage the ANE
field and returned broken values when use
ethtool -A|-a.

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