ath: regd: Provide description for ath_reg_apply_ir_flags's 'reg' param

Fixes the following W=1 kernel build warning(s):

drivers/net/wireless/ath/regd.c:378: warning: Function parameter or member 'reg' not described in 'ath_reg_apply_ir_flags'

Cc: Kalle Valo <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/net/wireless/ath/regd.c

···
 /**
  * ath_reg_apply_ir_flags()
  * @wiphy: the wiphy to use
+ * @reg: regulatory structure - used for country selection
  * @initiator: the regulatory hint initiator
  *
  * If no country IE has been received always enable passive scan