staging: wilc1000: use is_broadcast_ether_addr check for broadcast address

Make use of is_broadcast_ether_addr() to check if mac address is broadcast
address. Remove static 'broadcast', as its not needed after use of
is_broadcast_ether_addr().

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>