security: pfe: update data unit number for default key too

Default key will be used to encrypt the metadata of file
system. For metadata inode/bio file encryption type will be invalid
hence data unit number (dun) update in file system specific per file
key driver will not work.

Change-Id: Ib79c35d4b76be4b1cf3732673cc251bfca71f466
Signed-off-by: Neeraj Soni <neersoni@codeaurora.org>