jbd2: fix the comment of struct jbd2_journal_handle

the struct name was modified long ago, but the comment still
use struct handle_s.

Signed-off-by: Hui Su <sh_def@163.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200922171231.GA53120@rlk


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