Fixed some implicitly type conversions between vector and scalar data type.

There are some mixed implicitly/explicitly type conversion between
scalar and vector. Although the spec allows those conversion, I prefer
to make them consistent and use explicitly all the cases.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Merge pull request #1933 from gongzg:fix-ocl-kernel-2.4