net: fec: remove checking for NULL phy_dev in fec_enet_close()

fep->phy_dev can not be NULL here for two reasons:
- fec_enet_open() will have successfully connected the phy, or will have
  failed.
- fec_enet_open() will have called phy_start(fep->phy_dev), which
  unconditionally dereferences this pointer.

If it were to be NULL here, then fec_enet_open() will have already
oopsed.

Acked-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>