mISDN: remove unused variable 'faxmodulation_s'

drivers/isdn/hardware/mISDN/mISDNisar.c:30:17:
 warning: faxmodulation_s defined but not used [-Wunused-const-variable=]

It is never used, so can be removed.

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