Avoid incorrect flag when create ocl memory object.

If there is already a CL_MEM_USE_HOST_PTR, we should not
add CL_MEM_COPY_HOST_PTR. According to the OpenCL spec:
"
CL_MEM_COPY_HOST_PTR and
CL_MEM_USE_HOST_PTR are mutually exclusive.
"

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>