realtek: 5.15: fix compilation warning with PHY_INTERFACE_MODE_HSGMII

realtek: 5.15: fix compilation warning with PHY_INTERFACE_MODE_HSGMII

PHY_INTERFACE_MODE_HSGMII was not handled in phylink_get_linkmodes and
phylink_parse_mode.
Fix compilation warning by adding it in the enum:
drivers/net/phy/phylink.c: In function 'phylink_get_linkmodes':
drivers/net/phy/phylink.c:360:9: error: enumeration value 'PHY_INTERFACE_MODE_HSGMII' not handled in switch [-Werror=switch]
  360 |         switch (interface) {
      |         ^~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>