Fix comments that are used to print out the register functions

Author: HyukjinKwon

sql/core/src/main/scala/org/apache/spark/sql/UDFRegistration.scala

@@ -109,9 +109,10 @@ class UDFRegistration private[sql] (functionRegistry: FunctionRegistry) extends
          | * @since 1.3.0
          | */
          |def register(name: String, f: UDF$i[$extTypeArgs, _], returnType: DataType): Unit = {
+         |  val func = f$anyCast.call($anyParams)
          |  functionRegistry.registerFunction(
          |    name,
-         |    (e: Seq[Expression]) => ScalaUDF(f$anyCast.call($anyParams), returnType, e))
+         |    (e: Seq[Expression]) => ScalaUDF(func, returnType, e))
          |}""".stripMargin)
     }
     */