net: pcs: xpcs: Drop sentinel entry from 2500basex ifaces list

There are currently only two methods (xpcs_find_compat() and
xpcs_get_interfaces()) defined in the driver which loop over the available
interfaces. All of them rely on the xpcs_compat::num_interfaces field
value to get the total number of supported interfaces. Thus the interface
arrays are supposed to be filled with actual interface IDs and there is no
need in the dummy terminating ID placed at the end of the arrays.

Based on the above drop the PHY_INTERFACE_MODE_MAX entry from the
xpcs_2500basex_interfaces array and the PHY_INTERFACE_MODE_MAX-based
conditional statement from the xpcs_get_interfaces() method as redundant.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>