[SPARK-3953][SQL] Confusable variable name.

In SqlParser.scala, there is following code.

    case d ~ p ~ r ~ f ~ g ~ h ~ o ~ l  =>
      val base = r.getOrElse(NoRelation)
      val withFilter = f.map(f => Filter(f, base)).getOrElse(base)

In the code above, there 2 variables which has same name "f" in near place. 
One is receiver "f" and other is bound variable "f".