net: dsa: remove phy_disconnect from error path

The phy has not been initialized, disconnecting it in the error
path results in a NULL pointer exception. Drop the phy_disconnect
from the error path.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>