radeon: Fix VCE IB test on Big-Endian systems

This patch makes the VCE IB test pass on Big-Endian systems. It converts
to little-endian the contents of the VCE message.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>