drivers/net/usb: fix sparse warnings: Should it be static?

Impact: Make symbols static.

Fix this sparse warnings:
  drivers/net/usb/hso.c:1249:6: warning: symbol 'hso_unthrottle_tasklet' was not declared. Should it be static?
  drivers/net/usb/hso.c:1268:6: warning: symbol 'hso_unthrottle_workfunc' was not declared. Should it be static?
  drivers/net/usb/hso.c:1466:5: warning: symbol 'tiocmget_submit_urb' was not declared. Should it be static?
  drivers/net/usb/smsc95xx.c:62:5: warning: symbol 'turbo_mode' was not declared. Should it be static?

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