mac80211: ath9k: fix missing prototypes warnings

mac80211: ath9k: fix missing prototypes warnings

Fix following warnings by including the corresponding headers:

backports-6.12.6/drivers/net/wireless/ath/ath9k/hsr.c:50:6: error: no previous prototype for 'ath9k_hsr_init' [-Werror=missing-prototypes]
   50 | void ath9k_hsr_init(struct ath_hw *ah)
      |      ^~~~~~~~~~~~~~
backports-6.12.6/drivers/net/wireless/ath/ath9k/hsr.c:165:5: error: no previous prototype for 'ath9k_hsr_disable' [-Werror=missing-prototypes]
  165 | int ath9k_hsr_disable(struct ath_hw *ah)
      |     ^~~~~~~~~~~~~~~~~
backports-6.12.6/drivers/net/wireless/ath/ath9k/hsr.c:177:5: error: no previous prototype for 'ath9k_hsr_enable' [-Werror=missing-prototypes]
  177 | int ath9k_hsr_enable(struct ath_hw *ah, int bw, int fq)
      |     ^~~~~~~~~~~~~~~~
backports-6.12.6/drivers/net/wireless/ath/ath9k/hsr.c:234:5: error: no previous prototype for 'ath9k_hsr_status' [-Werror=missing-prototypes]
  234 | int ath9k_hsr_status(struct ath_hw *ah)
      |     ^~~~~~~~~~~~~~~~

Signed-off-by: Shiji Yang <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/18637
Signed-off-by: Hauke Mehrtens <[email protected]>