When MAC is not support PMT, driver will check PHY's WoL capability
and set device wakeup capability in stmmac_init_phy(). We can enable
the WoL through ethtool, the driver would enable the device wake up
flag. Now the device_may_wakeup() return true.

But if there is a way which enable the PHY's WoL capability derectly,
like in BIOS. The driver would not know the enable thing and would not
set the device wake up flag. The phy_suspend may failed like this:

[   32.409063] PM: dpm_run_callback(): mdio_bus_phy_suspend+0x0/0x50 returns -16
[   32.409065] PM: Device stmmac-1:00 failed to suspend: error -16
[   32.409067] PM: Some devices failed to suspend, or early wake event detected

Add to set the device wakeup enable flag according to the get_wol
function result in PHY can fix the error in this scene.

v2: add a Fixes tag.

Fixes: 1d8e5b0f ("net: stmmac: Support WOL with phy")
Signed-off-by: Rongguang Wei <weirongguang@kylinos.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>