net: fec: remove useless fep->opened

napi_disable() waits until the NAPI processing has completed, and then
prevents any further polls.  At this point, the driver then clears
fep->opened.  The NAPI poll function uses this to stop processing in
the receive path.  Hence, it will never see this variable cleared,
because the NAPI poll has to complete before it will be cleared.

Therefore, this variable serves no purpose, so let's remove it.

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>