text->patch: per comments on merge request

https://git.beagleboard.org/docs/docs.beagleboard.io/-/merge_requests/79#note_15599

books/beaglebone-cookbook/07kernel/kernel.rst

@@ -523,7 +523,7 @@ Solution
 .. _kernel_hello_patch:
 
 .. literalinclude:: ../code/07kernel/hello.patch
-   :language: text
+   :language: diff
    :caption: Simple kernel patch file (hello.patch)
    :linenos: