fix make <block> running all make blocks

Makefile

diff --git a/Makefile b/Makefile
index e787f93..f8f844c 100644
--- a/Makefile
+++ b/Makefile
@@ -65,7 +65,7 @@
 # Openlane
 blocks=$(shell cd openlane && find * -maxdepth 0 -type d)
 .PHONY: $(blocks)
-$(blocks):
+$(blocks): % :
 	export CARAVEL_ROOT=$(CARAVEL_ROOT) && cd openlane && $(MAKE) $*
 
 dv_patterns=$(shell cd verilog/dv && find * -maxdepth 0 -type d)