net: emacps: Fix gmii2rgmii_phy_dev disconnect

In xemacps_mii_probe(), when connecting lp->phy_node fails, clean up
and disconnect lp->gmii2rgmii_phy_dev [which may be already connected].

In xemacps_close(), check lp->gmii2rgmii_phy_dev before disconnecting
it, not lp->gmii2rgmii_phy_node.

Signed-off-by: Thomas Betker <thomas.betker@rohde-schwarz.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>