mwifiex: update adapter->bss_prio_tbl[j].bss_prio_cur correctly

"adapter->bss_prio_tbl[j].bss_prio_head" points to linked list of
interfaces with priority 'j'. "bss_prio_tbl[j].bss_prio_cur" is
supposed to point to next interface every time the routine for
dequeuing the packet is called. This ensures that each interface
gets fair chance.

Currently we have AP and station interfaces with priority '0'.
Therefore "adapter->bss_prio_tbl[0].bss_prio_cur" should
alternately point to AP and station nodes. Since "bss_prio_cur"
is not correctly updated, for each packet picked for AP, two
packets are picked for station interface.

This patch fixes the problem by correctly updating "bss_prio_cur".

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>