jbd2: remove unneeded kmap to do escape in jbd2_journal_write_metadata_buffer

The data to do escape could be accessed directly from b_frozen_data,
just remove unneeded kmap.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240514112438.1269037-6-shikemeng@huaweicloud.com


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