drivers/net: fix sparse warnings: make symbols static

Fix this sparse warnings:

  drivers/net/3c523.c:350:6: warning: symbol 'alloc586' was not declared. Should it be static?
  drivers/net/cs89x0.c:1029:14: warning: symbol 'reset_chip' was not declared. Should it be static?
  drivers/net/eepro.c:1399:1: warning: symbol 'read_eeprom' was not declared. Should it be static?
  drivers/net/plip.c:1020:5: warning: symbol 'plip_hard_header_cache' was not declared. Should it be static?
  drivers/net/s2io.c:5116:6: warning: symbol 'do_s2io_store_unicast_mc' was not declared. Should it be static?
  drivers/net/smc9194.c:767:12: warning: symbol 'smc_findirq' was not declared. Should it be static?

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