ath: Fix wrong function name in comments

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

 drivers/net/wireless/ath/hw.c:119: warning: expecting prototype for ath_hw_set_bssid_mask(). Prototype was for ath_hw_setbssidmask() instead

Signed-off-by: Yang Shen <shenyang39@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210517050141.61488-3-shenyang39@huawei.com