net: hamradio: use eth_broadcast_addr

The array bpq_eth_addr is only used to get the size of an
address, whereas the bcast_addr is used to set the broadcast
address. This leads to a warning when using clang:
drivers/net/hamradio/bpqether.c:94:13: warning: variable 'bpq_eth_addr' is not
      needed and will not be emitted [-Wunneeded-internal-declaration]
static char bpq_eth_addr[6];
            ^

Remove both variables and use the common eth_broadcast_addr
to set the broadcast address.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>