zdtm/make: return .PHONY for default

I don't why it is required here, but make doesn't work w/o it

make[2]: Leaving directory `<https://10.30.26.89/job/CRIU/ws/test/zdtm/live/static'>
make[1]: Leaving directory `<https://10.30.26.89/job/CRIU/ws/test/zdtm/live'>
set -e; for d in lib live; do make -C $d default; done
make[1]: Entering directory `<https://10.30.26.89/job/CRIU/ws/test/zdtm/lib'>
make[1]: *** No rule to make target `default'.  Stop.
make[1]: Leaving directory `<https://10.30.26.89/job/CRIU/ws/test/zdtm/lib'>
make: *** [default] Error 2
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm/Makefile

 SUBDIRS	=	lib live
 
 default:	all
+.PHONY: default
 
 %:
 	set -e; for d in $(SUBDIRS); do $(MAKE) -C $$d $@; done

test/zdtm/live/Makefile

 SUBDIRS	=	streaming transition static
 
 default:	all
+.PHONY: default
 
 %:
 	set -e; for d in $(SUBDIRS); do $(MAKE) -C $$d $@; done