docs(gatsby-plugin-mdx): fix error in MDXProvider component ref (#19075)

Author: alexluong

packages/gatsby-plugin-mdx/README.md

@@ -472,7 +472,7 @@ The following components can be customized with the MDXProvider:
 | `em`            | [Emphasis](https://github.com/syntax-tree/mdast#emphasis)            | `_emphasis_`                                        |
 | `strong`        | [Strong](https://github.com/syntax-tree/mdast#strong)                | `**strong**`                                        |
 | `delete`        | [Delete](https://github.com/syntax-tree/mdast#delete)                | `~~strikethrough~~`                                 |
-| `code`          | [InlineCode](https://github.com/syntax-tree/mdast#inlinecode)        |                                                     |
+| `inlineCode`    | [InlineCode](https://github.com/syntax-tree/mdast#inlinecode)        |                                                     |
 | `hr`            | [Break](https://github.com/syntax-tree/mdast#break)                  | `---`                                               |
 | `a`             | [Link](https://github.com/syntax-tree/mdast#link)                    | `<https://mdxjs.com>` or `[MDX](https://mdxjs.com)` |
 | `img`           | [Image](https://github.com/syntax-tree/mdast#image)                  | `![alt](https://mdx-logo.now.sh)`                   |