msm: eva: Copy back the validated size to avoid security issue

As we are reading the packet from a shared queue, there is a
possibility to corrupt the packet->size data of shared queue by
malicious FW after validating it in the kernel driver.

Change-Id: Ib9eed5e4155c67d155993ef4445d3fd2499b8b6f
Signed-off-by:  <ptak&lt;quic_ptak@quicinc.com>
(cherry picked from commit d735e9ea)