Improve end of expression check in for loop lints

The code should to check that the current expression _is_ the end
expression; not that it's equal to it. The equality check seems very
wasteful in terms of performance.

clippy_lints/src/loops.rs

@@ -2042,7 +2042,7 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
         if self.state == VarState::DontWarn {
             return;
         }
-        if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
+        if expr.hir_id == self.end_expr.hir_id {
             self.past_loop = true;
             return;
         }