staging: rtl8188eu: use eth_broadcast_addr() in place of memset

Replace the memset of array to broadcast address 0xFF by using the
eth_broadcast_addr() API

Signed-off-by: Hari Prasath Gujulan Elango <hgujulan@visteon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>