net: phy: Test previous phydev->dev against new mac dev

In phy_connect_dev(), if the phy device has an accociated mac device
before, a warning message will be printed. But we should test the
old device against the new one, if they are actually the same one,
don't print the warning message.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>