eth: mucse: rnpgbevf: initialize the variable 'advertising'

Fix follow error with clang-19:

drivers/net/ethernet/mucse/rnpgbevf/rnpgbevf_ethtool.c:143:3: error: variable 'advertising' is uninitialized when used here [-Werror,-Wuninitialized]
  143 |                 advertising |= ADVERTISED_FIBRE | ADVERTISED_1000baseKX_Full;
      |                 ^~~~~~~~~~~
drivers/net/ethernet/mucse/rnpgbevf/rnpgbevf_ethtool.c:131:28: note: initialize the variable 'advertising' to silence this warning
  131 |         u32 supported, advertising;
      |                                   ^
      |                                    = 0
1 error generated.

Signed-off-by: WangYuli <[email protected]>

drivers/net/ethernet/mucse/rnpgbevf/rnpgbevf_ethtool.c

@@ -128,7 +128,8 @@ static int rnpgbevf_get_link_ksettings(struct net_device *netdev,
 	struct rnpgbevf_hw *hw = &adapter->hw;
 	bool autoneg = false;
 	bool link_up;
-	u32 supported, advertising;
+	u32 supported;
+	u32 advertising = 0;
 	u32 link_speed = 0;
 
 	ethtool_convert_link_mode_to_legacy_u32(&supported,