hfsplus: fix "unused node is not erased" error

hfsplus: fix "unused node is not erased" error

Zero newly allocated extents in the catalog tree if volume attributes tell
us to.  Not doing so we risk getting the "unused node is not erased"
error.  See kHFSUnusedNodeFix flag in Apple's source code for reference.

There was a previous commit clearing the node when it is freed:
  commit 899bed05e9f6bbb21776f9ebd88f5631987f987a
  Author: Vyacheslav Dubeyko <slava@dubeyko.com>
  Date:   Wed Feb 27 17:03:06 2013 -0800
  hfsplus: fix issue with unzeroed unused b-tree nodes
It did not handle newly allocated extents (this patch fixes it). And it zeroed
nodes in all trees unconditionally which is an overkill. This patch adds a
condition and also switches to 'tree->node_size' as a simpler method of getting
the length to zero.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Cc: Anton Altaparmakov <aia21@cam.ac.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Hin-Tak Leung <htl10@users.sourceforge.net>
Cc: Kyle Laracey <kalaracey@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>