fix out of tree build

Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

Makefile

@@ -168,7 +168,7 @@ check-qjson: check-qjson.o $(qobject-obj-y) $(tools-obj-y)
 test-coroutine: test-coroutine.o qemu-timer-common.o async.o $(coroutine-obj-y) $(tools-obj-y)
 
 $(qapi-obj-y): $(GENERATED_HEADERS)
-qapi-dir := qapi-generated
+qapi-dir := $(SRC_PATH)/qapi-generated
 test-visitor.o test-qmp-commands.o qemu-ga$(EXESUF): QEMU_CFLAGS += -I $(qapi-dir)
 qemu-ga$(EXESUF): LIBS = $(LIBS_QGA)