drivers/net/wireless/ath9k: fix sparse warnings: Should it be static?

Impact: Make symbols static.

Fix this sparse warnings:
  drivers/net/wireless/ath9k/eeprom.c:1343:5: warning: symbol 'ath9k_hw_4k_get_spur_channel' was not declared. Should it be static?
  drivers/net/wireless/ath9k/eeprom.c:1372:19: warning: symbol 'eep_4k_ops' was not declared. Should it be static?
  drivers/net/wireless/ath9k/eeprom.c:2649:5: warning: symbol 'ath9k_hw_def_get_spur_channel' was not declared. Should it be static?
  drivers/net/wireless/ath9k/eeprom.c:2678:19: warning: symbol 'eep_def_ops' was not declared. Should it be static?

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