docs: temporarily disable the kernel-doc extension

Preserve bisectability while we update scripts/kernel-doc from Linux.
Without this patch, building with Sphinx 3 would break while we
revert our own Sphinx 3 support and replace it with Linux's.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/sphinx/kerneldoc.py

@@ -75,6 +75,9 @@ class KernelDocDirective(Directive):
         # Tell sphinx of the dependency
         env.note_dependency(os.path.abspath(filename))
 
+        # Disabled temporarily while scripts/kernel-doc is updated
+        return []
+
         tab_width = self.options.get('tab-width', self.state.document.settings.tab_width)
 
         # FIXME: make this nicer and more robust against errors