ASoC: msm: qdsp6v2: extend validation of virtual address

Validate a buffer virtual address is fully within the region before
returning the region to ensure functionality for an extended edge
case.

Change-Id: Iba3e080889980f393d6a9f0afe0231408b92d654
Signed-off-by: Siena Richard <sienar@codeaurora.org>
CRs-fixed: 1108461