net: qcom/emac: do not call emac_mac_start twice

emac_mac_start() uses information from the external PHY to program
the MAC, so it makes no sense to call it before the link is up.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>