realtek: RTL838x: remove artifical mdio delays

realtek: RTL838x: remove artifical mdio delays

For some reason 3 of the 4 mdio access functions contain an
artifical delay of 10ms. While it might have been part of
older Realtek SDKs it can no longer be found in current ones.
Remove the delays.

While we are here remove the pre-access bus ready checks.
It is sufficient to run them after the command start. If
anything fails the caller will get an error. This is the
same behaviour as for the other targets.

Finally cleanup the error handling. Something like this makes
no sense at all.

  err = rtmdio_838x_smi_wait_op(100000);
  if (err)
    goto errout;
  err = 0;
errout:

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/19901
Signed-off-by: Robert Marko <robimarko@gmail.com>