staging: rtl8188eu: rtw_set_fixed_ie(): accept void* parameters

rtw_set_ie() is a memcpy-like function, taking addresses of memory buffers
among its parameters. Similarly to memcpy, change the parameters to be
void*. This will allow to get rid of typecasts whenever it is called.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>