msm:audio: 7x27: Fix bug by releasing spinlock in error case

Audio drivers does not release spinlock when kmalloc() fails in
post_event function. This can result in deadlock or system hang
in low memory conditions. Fix this bug by releasing the spinlock
when kmalloc fails.

Change-Id: Id6ffd5c34ac36f68cb7b490a43bdf09bb80c5b9e
CRs-Fixed: 281588
Signed-off-by: Sriranjan Srikantam <cssrika@codeaurora.org>