amd-xgbe: fix mismatched prototype

The forward declaration was introduced with a prototype that does
not match the function definition:

drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c:2166:13: error: conflicting types for 'xgbe_phy_perform_ratechange' due to enum/integer mismatch; have 'void(struct xgbe_prv_data *, enum xgbe_mb_cmd, enum xgbe_mb_subcmd)' [-Werror=enum-int-mismatch]
2166 | static void xgbe_phy_perform_ratechange(struct xgbe_prv_data *pdata,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c:391:13: note: previous declaration of 'xgbe_phy_perform_ratechange' with type 'void(struct xgbe_prv_data *, unsigned int, unsigned int)'
391 | static void xgbe_phy_perform_ratechange(struct xgbe_prv_data *pdata,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Ideally there should not be any forward declarations here, which
would make it easier to show that there is no unbounded recursion.
I tried fixing this but could not figure out how to avoid the
recursive call.

As a hotfix, address only the broken prototype to fix the build
problem instead.

Fixes: 4f3b20bfbb75 ("amd-xgbe: add support for rx-adaptation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20230203121553.2871598-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>