doc/Makefile: fix epub and latexpdf targets

Fixing "make clean" followed by "make epub" or "make latexpdf"

(From yocto-docs rev: 0dac10fc3d170fb162f4df6547541071bfa7a94e)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/Makefile

@@ -47,9 +47,11 @@ clean:
 	@rm -rf $(BUILDDIR) $(PNGs) $(PDFs) poky.yaml sphinx-static/switchers.js
 
 epub: $(PNGs)
+	$(SOURCEDIR)/set_versions.py
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
 latexpdf: $(PDFs)
+	$(SOURCEDIR)/set_versions.py
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
 all: html epub latexpdf