regmap: debugfs: Ensure a correct return value for empty caches

This should never happen in the real world.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap-debugfs.c

@@ -116,6 +116,16 @@ static unsigned int regmap_debugfs_get_dump_start(struct regmap *map,
 		}
 	}
 
+	/*
+	 * This should never happen; we return above if we fail to
+	 * allocate and we should never be in this code if there are
+	 * no registers at all.
+	 */
+	if (list_empty(&map->debugfs_off_cache)) {
+		WARN_ON(list_empty(&map->debugfs_off_cache));
+		return base;
+	}
+
 	/* Find the relevant block */
 	list_for_each_entry(c, &map->debugfs_off_cache, list) {
 		if (from >= c->min && from <= c->max) {