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 currupt the packet->size data of shared queue by
mallicious FW after validating it in the kernel driver.

Change-Id: I9bff8f2daa64054eada37de54fe3fa837d57b22a
Signed-off-by: Aniruddh Sharma <quic_anirshar@quicinc.com>
Signed-off-by: Madhu Ananthula <quic_mananthu@quicinc.com>