net: phy: fix PHY_RUNNING in phy_state_machine

Currently, if phy state is PHY_RUNNING, we always register a CHANGE
when phy works in polling or interrupt ignored, this will make the
adjust_link being called even the phy link did Not changed.

checking the phy link to make sure the link did changed before we
register a CHANGE, if link did not changed, we do nothing.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>