wifi: ath11k: workaround too long expansion sparse warnings

In v6.7-rc1 sparse warns:

drivers/net/wireless/ath/ath11k/mac.c:4702:15: error: too long token expansion
drivers/net/wireless/ath/ath11k/mac.c:4702:15: error: too long token expansion
drivers/net/wireless/ath/ath11k/mac.c:8393:23: error: too long token expansion
drivers/net/wireless/ath/ath11k/mac.c:8393:23: error: too long token expansion

Workaround the warnings by refactoring the code to a new function, which also
reduces code duplication. And in the new function use max3() to make the code
more readable.

No functional changes, compile tested only.

Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20231214161740.1582340-1-kvalo@kernel.org