net: phy: smsc: Fix disabling energy detect mode

When the lan87xx_read_status function is getting called the
energy detect mode is enabled again even if it has been
disabled by device tree.

Added private struct to check the energy detect status.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: David S. Miller <davem@davemloft.net>