qcacmn: Fix packet offset computation logic in Tx path

Fix the packet offset value filled in Tx descriptor.
Also fix a crash in Tx completion handler because of storing wrong
pointer in tx descriptor chain (next)

CRs-Fixed: 1088985
Change-Id: Ie2895700e0bb7e6f4b7b09a01da07a17d1c41160
2 files changed