stubdom/Makefile: use QEMU_TRADITIONAL_LOC

In commit 8962a8f951 CONFIG_QEMU was
replaced by QEMU_TRADITIONAL_LOC. However stubdom/Makefile still uses
CONFIG_QEMU so building stubdom is likely to fail.  This patch
replaces CONFIG_QEMU with QEMU_TRADITIONAL_LOC in stubdom/Makefile as
well.

Signed-off-by: Michael Young <m.a.young@durham.ac.uk>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Release-Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

stubdom/Makefile

@@ -263,7 +263,7 @@ $(OCAML_STAMPFILE): ocaml-$(XEN_TARGET_ARCH)/.dirstamp
 .PHONY: $(CROSS_ROOT)
 $(CROSS_ROOT): cross-newlib cross-zlib cross-libpci
 
-QEMU_ROOT := $(shell if [ -d "$(CONFIG_QEMU)" ]; then echo "$(CONFIG_QEMU)"; else echo .; fi)
+QEMU_ROOT := $(shell if [ -d "$(QEMU_TRADITIONAL_LOC)" ]; then echo "$(QEMU_TRADITIONAL_LOC)"; else echo .; fi)
 
 ifneq ($(filter ioemu,$(STUBDOM_TARGETS)),)
 IOEMU_LINKFARM_TARGET := ioemu/linkfarm.stamp