fix issue when create cl image from libva with offset

fix issue when create cl image from libva with offset

to share data between libva and ocl (at drm level), it is acceptable
to create cl image from libva with offset (to drm object). Correct
the bo offset whose value will finally go to ss1.base_addr.

Signed-off-by: Guo Yejun <yejun.guo@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>