btrfs: polish names of kmem caches

Usecase:

  watch 'grep btrfs < /proc/slabinfo'

easy to watch all caches in one go.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index eb768c4..b26d2f9 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -29,7 +29,7 @@
 
 int __init btrfs_delayed_inode_init(void)
 {
-	delayed_node_cache = kmem_cache_create("delayed_node",
+	delayed_node_cache = kmem_cache_create("btrfs_delayed_node",
 					sizeof(struct btrfs_delayed_node),
 					0,
 					SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,