wifi: ath9k: remove TX99 power array zero init

wifi: ath9k: remove TX99 power array zero init

This array is fully initialized in the loop itself. No need to zero
initialize and then overwrite.

Remove static from the array. This was a holdover from when the array
was a static global variable. It no longer confers any benefit.

Also add a min() call to avoid the manual if/ternary operation.

Assisted-by: Codex:GPT-5.5
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260517222136.1660347-1-rosenp@gmail.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>