staging: r8188eu: remove HW_VAR_FIFO_CLEARN_UP

Remove the HW_VAR_FIFO_CLEARN_UP case from SetHwReg8188EU() and move
its functionality to a new static function in os_intfs.c. This is part
of the ongoing effort to get rid of the unwanted hal layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220409120627.10633-4-straube.linux@gmail.com


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