phylib: reset mii bus only if reset handler is registered

This change allows to cope with a mii bus device registered using
miiphy_register(), which doesn't assign a default reset handler.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Detlev Zundel <dzu@denx.de>

drivers/net/phy/phy.c

@@ -692,7 +692,8 @@ struct phy_device *phy_connect(struct mii_dev *bus, int addr,
 	struct phy_device *phydev;
 
 	/* Reset the bus */
-	bus->reset(bus);
+	if (bus->reset)
+		bus->reset(bus);
 
 	/* Wait 15ms to make sure the PHY has come out of hard reset */
 	udelay(15000);