kbuild: Less modules printed when warned about SUBDIRS usage

From: Rusty Russell <rusty@rustcorp.com.au>

Now kbuild prints out a line telling only what modules there are added,
not all modules.

scripts/Makefile.modpost

@@ -14,7 +14,7 @@ __modules := $(shell head -q -n1 /dev/null $(wildcard $(MODVERDIR)/*.mod))
 modules := $(patsubst %.o,%.ko,$(wildcard $(__modules:.ko=.o)))
 
 ifneq ($(filter-out $(modules),$(__modules)),)
-  $(warning Trouble: $(__modules) )
+  $(warning Trouble: $(filter-out $(modules),$(__modules)))
   $(warning *** Uh-oh, you have stale module entries. You messed with SUBDIRS,)
   $(warning     do not complain if something goes wrong.)
 endif