staging: rtl8723bs: Replace function odm_SignalScaleMapping()

Remove function odm_SignalScaleMapping as all it does is call
odm_SignalScaleMapping_92CSeries.
Rename odm_SignalScaleMapping_92CSeries to odm_SignalScaleMapping and
change its type from static to non-static to maintain compatibility with
call sites of odm_SignalScaleMapping.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>