Makefile: update location of target-specific .conf

arduino_101.conf was moved up a level, but the toplevel Makefile
was not updated so that it can be located.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
diff --git a/Makefile b/Makefile
index 25d06de..410ed4b 100644
--- a/Makefile
+++ b/Makefile
@@ -30,7 +30,7 @@
 BOARD ?= qemu_x86
 
 # Additional board-specific Zephyr configuration
-CONF_FILE += $(wildcard boot/zephyr/targets/$(BOARD).conf)
+CONF_FILE += $(wildcard boot/zephyr/$(BOARD).conf)
 
 # The source to the Zephyr-specific code lives here.
 SOURCE_DIR = boot/zephyr