ext4: use %pd printk specificer

Use the new %pd printk() specifier in Ext4 to replace passing of
dentry name or dentry name and name length * 2 with just passing the
dentry.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
cc: Andreas Dilger <adilger.kernel@dilger.ca>
cc: linux-ext4@vger.kernel.org