Apply suggestions from code review

Co-authored-by: Simon Friis Vindum <paldepind@github.com>

Author: geoffw0

rust/ql/lib/codeql/rust/elements/DerefExpr.qll

@@ -6,7 +6,7 @@ private import codeql.rust.elements.PrefixExpr
 private import codeql.rust.elements.Operation
 
 /**
- * A dereference expression, `*`.
+ * A dereference expression, the prefix operator `*`.
  */
 final class DerefExpr extends PrefixExpr, Operation {
   DerefExpr() { this.getOperatorName() = "*" }

rust/ql/lib/codeql/rust/security/AccessInvalidPointerExtensions.qll

@@ -50,7 +50,7 @@ module AccessInvalidPointer {
    * A pointer access using the unary `*` operator.
    */
   private class DereferenceSink extends Sink {
-    DereferenceSink() { exists(DerefExpr p | p.getExpr() = this.asExpr().getExpr()) }
+    DereferenceSink() { any(DerefExpr p).getExpr() = this.asExpr().getExpr() }
   }
 
   /**