stmmac: fix PLS bit setting when EEE is active

In case of PLS is active the PLS (PHY Link Status) bit in
the Reg12 has to be set to allow the MAC to asserts the LPI
pattern when the link is ok.

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