[libclc] libclc: clspv: update gen_convert.cl for clspv (PR #66902)

[Kévin Petit via cfe-commits]

================
@@ -251,13 +258,19 @@ def generate_default_conversion(src, dst, mode):
         print("#endif")
 
 
-for src in types:
-    for dst in types:
-        generate_default_conversion(src, dst, "")
+# Do not generate default conversion for clspv as they are handle natively
----------------
kpet wrote:

```suggestion
# Do not generate default conversion for clspv as they are handled natively
```

https://github.com/llvm/llvm-project/pull/66902