btrfs: add more __cold annotations

The __cold functions are placed to a special section, as they're
expected to be called rarely. This could help i-cache prefetches or help
compiler to decide which branches are more/less likely to be taken
without any other annotations needed.

Though we can't add more __exit annotations, it's still possible to add
__cold (that's also added with __exit). That way the following function
categories are tagged:

- printf wrappers, error messages
- exit helpers

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 41ab907..a335e2e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3378,7 +3378,7 @@ const struct file_operations btrfs_file_operations = {
 	.dedupe_file_range = btrfs_dedupe_file_range,
 };
 
-void btrfs_auto_defrag_exit(void)
+void __cold btrfs_auto_defrag_exit(void)
 {
 	kmem_cache_destroy(btrfs_inode_defrag_cachep);
 }