arch: ensure Cooja is built

Ensure the cd to the cooja directory
is successful before calling ant.

arch/cpu/msp430/Makefile.msp430

@@ -219,7 +219,7 @@ $(COOJA_PATH)/mspsim/build.xml: $(COOJA_PATH)/build.xml
 	@echo '----------------'
 
 $(COOJA_PATH)/mspsim/mspsim.jar: $(COOJA_PATH)/mspsim/build.xml
-	(cd $(COOJA_PATH)/mspsim && ant jar)
+	cd $(COOJA_PATH)/mspsim && ant jar
 
 %.mspsim:	%.${TARGET} ${COOJA_PATH}/mspsim/mspsim.jar
 	java -jar ${COOJA_PATH}/mspsim/mspsim.jar -platform=${TARGET} $<

arch/platform/cooja/Makefile.cooja

@@ -24,7 +24,7 @@ ifdef QUICKSTART
 # Create COOJA JAR rule
 $(COOJA_DIR)/dist/cooja.jar:
 	@echo "Creating COOJA Java archive..."
-	(cd $(COOJA_DIR) && ant jar)
+	cd $(COOJA_DIR) && ant jar
 
 # Quickstart rule
 ifneq ($(MAKECMDGOALS),clean)