[llvm] [ADT][NFC] Fix documentation for arrayRefFromStringRef (PR #203430)

[Sven van Haastregt via llvm-commits]

================
@@ -63,7 +63,7 @@ inline StringRef toStringRef(ArrayRef<char> Input) {
   return StringRef(Input.begin(), Input.size());
 }
 
-/// Construct a string ref from an array ref of unsigned chars.
+/// Construct an array ref of unsigned bytes from a string ref.
----------------
svenvh wrote:

```suggestion
/// Construct an array ref of bytes from a string ref.
```
as `signed char` is also valid for `CharT`.

https://github.com/llvm/llvm-project/pull/203430