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

Fix this sparse warnings:

  drivers/net/wireless/airo.c:3610:6: warning: symbol 'mpi_receive_802_11' was not declared. Should it be static?
  drivers/net/wireless/atmel.c:3183:6: warning: symbol 'atmel_join_bss' was not declared. Should it be static?
  drivers/net/wireless/ray_cs.c:831:5: warning: symbol 'ray_dev_init' was not declared. Should it be static?

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