ext4: remove unnecessary assignment in ext4_htree_store_dirent()

We have allocated memory using kzalloc() so don't have
to set 0 again in last byte.

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Link: https://lore.kernel.org/r/20191206054317.3107-1-cgxu519@mykernel.net


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