wil6210: set vring index for all descriptors

The vring index (MAC queue id) must be set in all TX descriptors
otherwise HW will fail to release descriptors for a specific vring
(disconnect or vring switch flows).
This is normally occurs when fragmentation required, if vring index
will not be the same for all SKB descriptors HW will fail to flush
this MAC queue.

Signed-off-by: Kirshenbaum Erez <erezk@wilocity.com>
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>