hamradio: bpqether: Fix -Wunused-const-variable warning

If CONFIG_PROC_FS is n, gcc warns:

drivers/net/hamradio/bpqether.c:437:36:
 warning: ‘bpq_seqops’ defined but not used [-Wunused-const-variable=]
 static const struct seq_operations bpq_seqops = {
                                    ^~~~~~~~~~
Use #ifdef macro to gurad this.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>