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: I3aae85dea560e2805e7bff2c48d4be763da597de
Signed-off-by: Gopireddy Arunteja Reddy <quic_garuntej@quicinc.com>