ext4: remove duplicate call to ext4_bread() in ext4_init_new_dir()

This fixes a buffer cache leak when creating a directory, introduced
in commit a774f9c2.

Signed-off-by: Guo Chao <yan@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Tao Ma <boyu.mt@taobao.com>