ext4: cleanup zeroout in ext4_split_extent_at()

ext4: cleanup zeroout in ext4_split_extent_at()

zero_ex is a temporary variable used only for writing zeros and
inserting extent status entry, it will not be directly inserted into the
tree. Therefore, it can be assigned values from the target extent in
various scenarios, eliminating the need to explicitly assign values to
each variable individually.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Message-ID: <20251129103247.686136-9-yi.zhang@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>