Fix compilation warning for PHY_INTERFACE_MODE_2500SGMII patch.
Fix compilation warning:
drivers/net/phy/phylink.c: In function 'phylink_get_linkmodes':
drivers/net/phy/phylink.c:360:9: error: enumeration value 'PHY_INTERFACE_MODE_2500SGMII' not handled in switch [-Werror=switch]
360 | switch (interface) {
| ^~~~~~
cc1: all warnings being treated as errors
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>