staging: rtl8188eu: don't cast to void* when calling memset()

The first argument to memset() is (void *), the explicit typecasts are
not needed. They just make code less readable.

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