OCL: fix for cv::memopTypeToStr

check_regression=OCL*Bitwise:OCL*Repeat:OCL*SetIden:OCL*Flip:OCL*Resize
test_modules=core,imgproc
test_filter=OCL*Bitwise:OCL*Repeat:OCL*SetIden:OCL*Flip:OCL*Resize
build_examples=OFF