fs/hfsplus/attributes.c: add __init to hfsplus_create_attr_tree_cache()

hfsplus_create_attr_tree_cache is only called by __init init_hfsplus_fs

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Reviewed-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>