mwifiex: remove_bss_prio_lock

This patch does away with spinlock in
mwifiex_wmm_get_highest_priolist_ptr in order to improve TP.

Signed-off-by: Zhaoyang Liu <liuzy@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>