msm: ipa: Fix race condition head_desc_list variable access

Protect the common shared sys head_desc_list with
spin lock to avoid the race condition.

Change-Id: I427374ef44f150d6ead4aa44e245b23a55b7dd9e
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>