realtek: pcs: rtl930x: improve error propagation

realtek: pcs: rtl930x: improve error propagation

Previous changes refactored the hardware mode configuration for RTL930x
a lot. Now that this is in a better shape, one issue persists: missing
error propagation. Only parts of this function really propagate an
error, others are silently dropped. While this is a known driver-wide
issue, at least make it good here. Propagate the errors from functions
which apply configuration sequences to the caller.

Single writes are still left out on purpose, they need and will be
addressed later.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22582
Signed-off-by: Robert Marko <robimarko@gmail.com>