drivers/net/tokenring: fix sparse warnings: make symbols static

Fix this sparse warnings:

  drivers/net/tokenring/ibmtr.c:1840:6: warning: symbol 'tok_rerun' was not declared. Should it be static?
  drivers/net/tokenring/madgemc.c:469:16: warning: symbol 'madgemc_setnselout_pins' was not declared. Should it be static?
  drivers/net/tokenring/proteon.c:286:16: warning: symbol 'proteon_setnselout_pins' was not declared. Should it be static?
  drivers/net/tokenring/skisa.c:303:16: warning: symbol 'sk_isa_setnselout_pins' was not declared. Should it be static?

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