jbd2: Fixup stale comment in commit code

jbd2_journal_next_log_block() does not look at
transaction->t_outstanding_credits. Remove the misleading comment.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191105164437.32602-2-jack@suse.cz


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