ext4: refactor initialize_dirent_tail()

Move the calculation of the location of the dirent tail into
initialize_dirent_tail().  Also prefix the function with ext4_ to fix
kernel namepsace polution.

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

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5b86df7..83128bd 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3147,8 +3147,8 @@ extern struct ext4_dir_entry_2 *ext4_init_dot_dotdot(struct inode *inode,
 				 struct ext4_dir_entry_2 *de,
 				 int blocksize, int csum_size,
 				 unsigned int parent_ino, int dotdot_real_len);
-extern void initialize_dirent_tail(struct ext4_dir_entry_tail *t,
-				   unsigned int blocksize);
+extern void ext4_initialize_dirent_tail(struct buffer_head *bh,
+					unsigned int blocksize);
 extern int ext4_handle_dirty_dirblock(handle_t *handle, struct inode *inode,
 				      struct buffer_head *bh);
 extern int ext4_ci_compare(const struct inode *parent,