zephyr: Replace DT_FLASH_DEV_NAME with DT_CHOSEN_ZEPHYR_FLASH_CONTROLLER_LABEL

As upstream zephyr is phasing out DT_FLASH defines for non-partition
usage replace DT_FLASH_DEV_NAME with
DT_CHOSEN_ZEPHYR_FLASH_CONTROLLER_LABEL.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/boot/zephyr/flash_map_extended.c b/boot/zephyr/flash_map_extended.c
index b2de884..4723af1 100644
--- a/boot/zephyr/flash_map_extended.c
+++ b/boot/zephyr/flash_map_extended.c
@@ -17,7 +17,7 @@
 
 MCUBOOT_LOG_MODULE_DECLARE(mcuboot);
 
-#if (!defined(CONFIG_XTENSA) && defined(DT_FLASH_DEV_NAME))
+#if (!defined(CONFIG_XTENSA) && defined(DT_CHOSEN_ZEPHYR_FLASH_CONTROLLER_LABEL))
 #define FLASH_DEVICE_ID SOC_FLASH_0_ID
 #define FLASH_DEVICE_BASE CONFIG_FLASH_BASE_ADDRESS
 #elif (defined(CONFIG_XTENSA) && defined(DT_JEDEC_SPI_NOR_0_LABEL))