mwifiex: replace ra_list_curr by list rotation.

After a packet is successfully transmitted, ra list is rotated, so the ra
next to the one transmitted, will be the first in the list. This way we
pick the ra' in a round robin fashion. This significantly simplifies
iteration in  mwifiex_wmm_get_highest_priolist_ptr to a call to
list_for_each_entry.
List rotation is done via list_move, where the head itself is temporarily
removed and then re-inserted after the item just transferred.

Signed-off-by: Andreas Fenkart <andreas.fenkart@streamunlimited.com>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>