rtl8712: remove useless calls to memset().

These calls are followed by calls to memcpy() on the same memory area, so they
can be safely removed.

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>