zephyr: convert DT_JEDEC_SPI_NOR_0_LABEL to new dt macros

As the DT define DT_JEDEC_SPI_NOR_0_LABEL is intended to be deprecated
move to the new macro style to determine for DT_JEDEC_SPI_NOR_0_LABEL

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/boot/zephyr/main.c b/boot/zephyr/main.c
index ce62851..c3e4cfe 100644
--- a/boot/zephyr/main.c
+++ b/boot/zephyr/main.c
@@ -284,9 +284,9 @@
         while (1)
             ;
     }
-#elif (defined(CONFIG_XTENSA) && defined(DT_JEDEC_SPI_NOR_0_LABEL))
-    if (!flash_device_get_binding(DT_JEDEC_SPI_NOR_0_LABEL)) {
-        BOOT_LOG_ERR("Flash device %s not found", DT_JEDEC_SPI_NOR_0_LABEL);
+#elif (defined(CONFIG_XTENSA) && defined(JEDEC_SPI_NOR_0_LABEL))
+    if (!flash_device_get_binding(JEDEC_SPI_NOR_0_LABEL)) {
+        BOOT_LOG_ERR("Flash device %s not found", JEDEC_SPI_NOR_0_LABEL);
         while (1)
             ;
     }