stmmac: request_irq when use an ext wake irq line (v2)

In case of we use an external Wake-Up IRQ line
(priv->wol_irq != dev->irq) we need to invoke the
request_irq.

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