ath9k: make array voice_priority static const

Don't populate the read-only array voice_priority on the stack but
instead make it static const. Also makes the object code a little
smaller.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220222121749.87513-1-colin.i.king@gmail.com