soc: qcom: bam_dmux: Fix pointer access after free issue

The rx skb pointer contains the bam dmux channel id and dereference skb
pointer to get the bam dmux channel information. In fail cases the channel
id is deference from the free skb result in bad memory access.

Cache the bam dmux channel id locally to avoid the accessing from invalid
pointer.

CRs-Fixed: 717621
Change-Id: I4775c6f04d4737a08716ba06209aa00e2b2116b9
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>