net: phy: exported the genphy_read_master_slave function

genphy_read_master_slave function allows to configure the master/slave
for gigabit phys only. In order to use this function irrespective of
speed, moved the speed check to the genphy_read_status call.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>