drivers/isdn/hardware/mISDN: fix sparse warnings: make symbols static

Fix this sparse warnings:
  drivers/isdn/hardware/mISDN/hfcpci.c:59:19: warning: symbol 'hfc_tl' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcpci.c:60:9: warning: symbol 'hfc_jiffies' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.h:201:6: warning: symbol 'conf_str' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.h:319:12: warning: symbol 'HFC_TE_LAYER1_STATES' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.h:331:12: warning: symbol 'HFC_NT_LAYER1_STATES' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.c:38:12: warning: symbol 'hfcsusb_rev' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.c:978:1: warning: symbol 'fill_isoc_urb' was not declared. Should it be static?
  drivers/isdn/hardware/mISDN/hfcsusb.c:1724:1: warning: symbol 'setup_hfcsusb' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>