gnu: linux-libre-documentation: Fix compilation.

When compiling linux-libre-documentation@6.6.16, the compilation fails with
following error message:

------
    Exception occurred:
      File "/tmp/guix-build-linux-libre-documentation-6.6.16.drv-0/linux-6.6.16/Documentation/sphinx/kernel_feat.py", line 112, in run
        nodeList = self.nestedParse(out_lines, fname)
    UnboundLocalError: local variable 'fname' referenced before assignment
------

This is already fixed upstream[0], so this commit backports the change.

0: https://lore.kernel.org/all/20240206054907.066a0325@coco.lan/t/

* gnu/packages/linux.scm (linux-libre-documentation): Apply patch fixing
compilation.

Change-Id: Ic96f14aa25df09f38e029ca70d2647cbf37c2365
Signed-off-by: Leo Famulari <leo@famulari.name>

gnu/packages/linux.scm

@@ -2004,6 +2004,17 @@ GnuPG-based password manager like @code{pass}.")
   (package
     (inherit linux-libre)
     (name "linux-libre-documentation")
+    (source
+     (origin
+       (inherit linux-libre-source)
+       (patches
+        (list
+         (origin
+           (method url-fetch)
+           (uri "https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/Documentation/sphinx/kernel_feat.py?id=c23de7ceae59e4ca5894c3ecf4f785c50c0fa428")
+           (sha256
+            (base32
+             "0inw2pl7nh82sw8bhvvzqa61552bisl78yc1nyl2x6dmpyppzrld")))))))
     (arguments
      (list
       #:tests? #f