This fixes this sparse warning:

  CHECK   drivers/net/wireless/ath/key.c
drivers/net/wireless/ath/key.c:110:6: warning: symbol
'ath_hw_set_keycache_entry' was not declared. Should it be static?
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>