msm: ocmem: Fix device addresses returned to Video subsystem.

Venus Core accesses into OCMEM via OCMEMNOC use relative
addressing mode instead of absolute addressing. Update the
OCMEM model to reflect this behavior.

Change-Id: I2c9bd63f350511720a894aefc7e044e1adf3047f
Signed-off-by: Naveen Ramaraj <nramaraj@codeaurora.org>