Typo: Fow -> For

Author: Andrew Ash <andrew@andrewash.com>

Closes #14563 from ash211/patch-8.

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

@@ -820,7 +820,7 @@ object functions {
 
   /**
    * Window function: returns the ntile group id (from 1 to `n` inclusive) in an ordered window
-   * partition. Fow example, if `n` is 4, the first quarter of the rows will get value 1, the second
+   * partition. For example, if `n` is 4, the first quarter of the rows will get value 1, the second
    * quarter will get 2, the third quarter will get 3, and the last quarter will get 4.
    *
    * This is equivalent to the NTILE function in SQL.