f2fs: Updates from Upstream

Till this commit (included)
f2fs: fix wrong casting for dentry name - http://git.kernel.org/cgit/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=linux-3.4&id=3304b56401c4509ffaa74705b49edc9e13cee195

Change-Id: Ic35d8dd4cd63af9bb919cb30add3f7b2d23bdaba
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>