Use DECLARE_FLEX_ARRAY() helper in drivers/md/bcache/bcache_ondisk.h

[GustavoARSilva]

diff -u -p ./drivers/md/bcache/bcache_ondisk.h /tmp/nothing/drivers/md/bcache/bcache_ondisk.h
--- ./drivers/md/bcache/bcache_ondisk.h
+++ /tmp/nothing/drivers/md/bcache/bcache_ondisk.h
@@ -360,7 +360,6 @@ struct jset {

        union {
                struct bkey     start[0];
-               __u64           d[0];
        };
 };

@@ -425,7 +424,6 @@ struct bset {

        union {
                struct bkey     start[0];
-               __u64           d[0];
        };
 };