staging: r8188eu: merge two signal scale mapping functions

Keep the odm_SignalScaleMapping function and remove
odm_SignalScaleMapping_92CSeries.

Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211006090949.1694-4-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>