Docs: Add missing variable reference for wp_edit_form_attachment_display.

This adds the missing `$post` reference in the inline docblock for
the `wp_edit_form_attachment_display` hook after [37879].

Props DrewAPicture.
See 36052.
Built from https://develop.svn.wordpress.org/trunk@37880


git-svn-id: http://core.svn.wordpress.org/trunk@37821 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/media.php

@@ -2773,7 +2773,7 @@ function edit_form_image_editor( $post ) {
 		 *
 		 * @since 4.6.0
 		 *
-		 * @param WP_Post A post object.
+		 * @param WP_Post $post A post object.
 		 */
 		do_action( 'wp_edit_form_attachment_display', $post );