wifi: rtw88: pci: Use enum type for rtw_hw_queue_mapping() and ac_to_hwq

rtw_hw_queue_mapping() and ac_to_hwq[] hold values of type enum
rtw_tx_queue_type. Change their types to reflect this to make it easier
to understand this part of the code.

While here, also change the array to be static const as it is not
supposed to be modified at runtime.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230204233001.1511643-2-martin.blumenstingl@googlemail.com