storage: flash_map: use DT_LABEL macro

Change code to use DT_LABEL macro so its more obvious what is going on.

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

include/zephyr/storage/flash_map.h

@@ -258,7 +258,7 @@ uint8_t flash_area_erased_val(const struct flash_area *fa);
 	DT_HAS_FIXED_PARTITION_LABEL(label)
 
 #define FLASH_AREA_LABEL_STR(lbl) \
-	DT_PROP(DT_NODE_BY_FIXED_PARTITION_LABEL(lbl), label)
+	DT_LABEL(DT_NODE_BY_FIXED_PARTITION_LABEL(lbl))
 
 #define FLASH_AREA_ID(label) \
 	DT_FIXED_PARTITION_ID(DT_NODE_BY_FIXED_PARTITION_LABEL(label))