net: qcom/emac: fix double free of SGMII IRQ during shutdown

If the interface is not up, then don't try to close it during a
shutdown.  This avoids possible double free of the IRQ, which
can happen during a shutdown.

Fixes: 03eb3eb4

 ("net: qcom/emac: add shutdown function")
Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>