net/phy/cortina.c: Update get_phy_id implementation

net/phy/cortina.c: Update get_phy_id implementation

Update get_phy_id() implementation in cortina.c to check
for Cortina_phy by comparing device phy_id with cortina phy_id
instead of relying on presence of CORTINA macros.

This will allow get_phy_id to work with non-cortina phy devices
which might have same phy address as Cortina device but on
different  bus.

Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>