Fix suggestions for &a: T parameters

Previously we were suggesting stuff like `fn f( &u32) {}`

src/test/ui/pattern/for-loop-bad-item.stderr

@@ -5,10 +5,14 @@ LL |     for ((_, _), (&mut c, _)) in &mut map {
    |                   ^^^^^^         -------- this is an iterator with items of type `(&(char, char), &mut (char, char))`
    |                   |
    |                   expected `char`, found `&mut _`
-   |                   help: you can probably remove the explicit borrow: `c`
    |
    = note:           expected type `char`
            found mutable reference `&mut _`
+help: consider removing `&mut` from the pattern
+   |
+LL -     for ((_, _), (&mut c, _)) in &mut map {
+LL +     for ((_, _), (c, _)) in &mut map {
+   | 
 
 error[E0308]: mismatched types
   --> $DIR/for-loop-bad-item.rs:14:14