staging: r8188eu: remove secondary_ch_offset_to_hal_ch_offset()

Function secondary_ch_offset_to_hal_ch_offset() is not used, remove
it.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210922200420.9693-34-straube.linux@gmail.com


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