docs: fix broken paths to docs/devel/qapi-code-gen.txt

With the move of some docs to docs/interop on ac06724a71,
a couple of references were not updated.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
5 files changed