Have cscope look in subdirs too

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/Makefile b/Makefile
index 978f8b2..288480f 100644
--- a/Makefile
+++ b/Makefile
@@ -65,7 +65,7 @@
 	-rm -f .depend cscope.out $(OBJS) $(PROGS) core.* core
 
 cscope:
-	@cscope -b
+	@cscope -b -R
 
 install: $(PROGS) $(SCRIPTS)
 	$(INSTALL) -m755 -d $(DESTDIR)$(bindir)