msm: ipa4: Removing the spin lock in irq context

In IRQ context head_desc_list protection was not required.
Removing the spin lock from IRQ context.

Change-Id: I37b0c69a97a2ce8b9bdba88b33c987bd19c76082
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>