realtek: pcs: rtl931x: fix clearing symbol errors

realtek: pcs: rtl931x: fix clearing symbol errors

Fix the implementation to clear symbol errors. Up to now, it was barely
functional because important modes weren't handled. Add another function
(which is needed in the future anyway) and pick to missing bits from
that function into the symbol clearing function to handle the modes
1000Base-X and 10GBaseR too. All that is based on [1].

While at it, rename the function to adhere to a common naming scheme and
fix some minor style issues.

[1] https://github.com/plappermaul/realtek-doc/blob/69d2890a2e2d7a03df6e40e2cd2c32ff5b074dcf/sources/rtk-dms1250/src/hal/phy/phy_rtl9310.c#L703

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/20736
Signed-off-by: Robert Marko <robimarko@gmail.com>