soc: qcom: bam_dmux: Fix race condition between close and notify_all

In power collapse state the msm_bam_dmux_close function make the link
up to send the close command to A2. Once the link is up notify callback
function is called for all open channels. There is a small window that
to can cause a race condition between notify_all and msm_bam_dmux_close.

Add spin_lock protection for bam_ch global strcture to avoid race
condition.

CRs-Fixed: 688437
Change-Id: I88f4a740770da662e63e1e492104b4752bf83e52
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>