py: Add order-only dependency for py-version.h

Else the directory might not exist.
Signed-off-by: Sven Wegener <sven.wegener@stealer.net>

py/py.mk

@@ -123,7 +123,7 @@ PY_O = $(addprefix $(PY_BUILD)/, $(PY_O_BASENAME))
 FORCE:
 .PHONY: FORCE
 
-$(HEADER_BUILD)/py-version.h: FORCE
+$(HEADER_BUILD)/py-version.h: FORCE | $(HEADER_BUILD)
 	$(Q)$(PY_SRC)/py-version.sh > $@.tmp
 	$(Q)if [ -f "$@" ] && cmp -s $@ $@.tmp; then rm $@.tmp; else echo "Generating $@"; mv $@.tmp $@; fi