staging: rtl8188eu: Use eth_broadcast_addr() to assign broadcast address

Simplify the code by using eth_broadcast_addr() to assign broadcast
address and removing the unnecessary variable bc_addr.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Link: https://lore.kernel.org/r/20210609085650.1269008-2-liushixin2@huawei.com


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