of: mdio: preserve phy dev_flags in of_phy_connect()

Replace assignment "=" with OR "|=" for "phy->dev_flags" so "dev_flags"
configured in phy probe() function can be preserved.

The idea is similar to commit e7312efbd5de ("net: phy: modify assignment
to OR for dev_flags in phy_attach_direct").

Signed-off-by: Tao Ren <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/of/of_mdio.c

···
 	if (!phy)
 		return NULL;
 
-	phy->dev_flags = flags;
+	phy->dev_flags |= flags;
 
 	ret = phy_connect_direct(dev, phy, hndlr, iface);