dm writecache: fix flexible_array.cocci warnings

Zero-length and one-element arrays are deprecated, see
Documentation/process/deprecated.rst
Flexible-array members should be used instead.

Generated by: scripts/coccinelle/misc/flexible_array.cocci

CC: Denis Efremov <efremov@linux.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-writecache.c

@@ -73,7 +73,7 @@ struct wc_memory_superblock {
 		};
 		__le64 padding[8];
 	};
-	struct wc_memory_entry entries[0];
+	struct wc_memory_entry entries[];
 };
 
 struct wc_entry {