docs(material/core): fix wrong mixin name (angular#25067)

* fix(docs/typography-guide): Defining a level

* Merge pull request #1 from atrawally/typography-docs-bug

fix(docs/typography-guide): Defining a level

Author: atrawally

guides/typography.md

@@ -61,7 +61,7 @@ table below.
 
 ### Define a level
 
-You can define a typography level with the `define-typography-config` Sass function. This function
+You can define a typography level with the `define-typography-level` Sass function. This function
 accepts, in order, CSS values for `font-size`, `line-height`, `font-weight`, `font-family`, and
 `letter-spacing`. You can also specify the parameters by name, as demonstrated in the example below.