rust: str: fix requierments->requirements typo

Fix a trivial spelling error in the `rust/kernel/str.rs` file.

Fixes: 247b365d ("rust: add `kernel` crate")
Reported-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/978Signed-off-by: Patrick Blass <patrickblass@mailbox.org>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
[Reworded slightly]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/str.rs

@@ -408,7 +408,7 @@ fn new() -> Self {
     /// If `pos` is less than `end`, then the region between `pos` (inclusive) and `end`
     /// (exclusive) must be valid for writes for the lifetime of the returned [`RawFormatter`].
     pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
-        // INVARIANT: The safety requierments guarantee the type invariants.
+        // INVARIANT: The safety requirements guarantee the type invariants.
         Self {
             beg: pos as _,
             pos: pos as _,