tests: $(BUILT_SOURCES) is not defined, depend on osmo-pcu

Change-Id: I6620a524b393a0db6201930a1e2795a439785824
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 1c7b072..00dc595 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -247,12 +247,12 @@
 
 # Python testing
 if ENABLE_VTY_TESTS
-python-tests: $(BUILT_SOURCES)
+python-tests: $(top_builddir)/src/osmo-pcu
 	osmotestvty.py -p $(abs_top_srcdir) -w $(abs_top_builddir) -v
 	osmotestconfig.py -p $(abs_top_srcdir) -w $(abs_top_builddir) -v
 
 else
-python-tests: $(BUILT_SOURCES)
+python-tests:
 	@echo "Not running python-based tests (determined at configure-time)"
 endif