mwifiex: make read-only array wmm_oui static const

Don't populate the read-only array wmm_oui 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>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220311225610.10895-1-colin.i.king@gmail.com