adsprpc: update mmap list nodes before mmap free

Update mmap list links before every mmap free.

Change-Id: Icb612a329e8defd65414842bae20f459c02364b9
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>