po/Makefile: Fix dependency for %.mo

Otherwise make will refuse to build updated .po files.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

po/Makefile

diff --git a/po/Makefile b/po/Makefile
index 8297ab5..60ccd7d 100644
--- a/po/Makefile
+++ b/po/Makefile
@@ -30,7 +30,7 @@
 	    $(INSTALL) -m644 $$obj $(DESTDIR)$(prefix)/share/locale/$$base/LC_MESSAGES/qemu.mo; \
 	done
 
-%.mo:
+%.mo: %.po
 	@msgfmt -o $@ $(SRC_PATH)/po/`basename $@ .mo`.po
 
 messages.po: $(SRC_PATH)/ui/gtk.c