staging: r8188eu: remove _ps_open_RF

The _ps_open_RF function is empty. Remove it.

Reviewed-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211126130400.26151-3-martin@kaiser.cx


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