rust: str: fix typo in comment

Fix a typo ("then" to "than") in a comment.

Signed-off-by: Jihed Chaibi <jihed.chaibi.dev@gmail.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Fixes: fffed67 ("rust: str: add `Formatter` type")
Link: https://lore.kernel.org/r/20250517002604.603223-1-jihed.chaibi.dev@gmail.com
[ Reworded. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: Jihed Chaibi

rust/kernel/str.rs

@@ -752,7 +752,7 @@ impl RawFormatter {
     /// for the lifetime of the returned [`RawFormatter`].
     pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
         let pos = buf as usize;
-        // INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
+        // INVARIANT: We ensure that `end` is never less than `buf`, and the safety requirements
         // guarantees that the memory region is valid for writes.
         Self {
             pos,