[POWERPC] bootwrapper: CONFIG_ -> CONFIG_DEVICE_TREE

A usage of CONFIG_DEVICE_TREE got accidentally truncated; this
fix allows out-of-tree dts files to work.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/boot/Makefile

@@ -166,7 +166,7 @@ cuboot-plat-$(CONFIG_83xx) += 83xx
 cuboot-plat-$(CONFIG_85xx) += 85xx
 cuboot-plat-y += unknown-platform
 
-dts = $(if $(shell echo $(CONFIG_) | grep '^/'),\
+dts = $(if $(shell echo $(CONFIG_DEVICE_TREE) | grep '^/'),\
        ,$(srctree)/$(src)/dts/)$(CONFIG_DEVICE_TREE)
 
 $(obj)/cuImage: vmlinux $(wrapperbits)