realtek: pcs: rtl930x: adjust initial vth_min value

realtek: pcs: rtl930x: adjust initial vth_min value

During RX calibration we use a vth_min value of 0 while the SDK always
uses a value of 1 [1]. While we do not know right now which effect this
really has, sync this to the SDK. In worst case we might have an
insufficient calibration result at the moment which usually might be
fine.

[1] https://github.com/plappermaul/realtek-doc/blob/82af3a36b7f65dbe2158fef3a9b71e7aab94315e/sources/rtk-dms1250/src/dal/longan/dal_longan_sds.c#L173

Suggested-by: Bevan Weiss <bevan.weiss@gmail.com>
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22450
Signed-off-by: Robert Marko <robimarko@gmail.com>