ext4 crypto: teach ext4_htree_store_dirent() to store decrypted filenames

ext4 crypto: teach ext4_htree_store_dirent() to store decrypted filenames

For encrypted directories, we need to pass in a separate parameter for
the decrypted filename, since the directory entry contains the
encrypted filename.

Change-Id: I2d1a78e65cb81152cae108ce7faadc28b52e0abe
Signed-off-by: Theodore Ts'o <tytso@mit.edu>