Fix one more typo

Author: HyukjinKwon

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala

@@ -1191,7 +1191,7 @@ case class ParseToDate(left: Expression, format: Option[Expression], child: Expr
  */
 @ExpressionDescription(
   usage = """
-    _FUNC_(timestamp[, fmt]) - Parses the `timestamp` expression with the `format` expression to
+    _FUNC_(timestamp[, fmt]) - Parses the `timestamp` expression with the `fmt` expression to
       a timestamp. Returns null with invalid input. By default, it follows casting rules to
       a timestamp if the `fmt` is omitted.
   """,