jbd2: Reorganize jbd2_journal_stop()

Move code in jbd2_journal_stop() around a bit. It removes some
unnecessary code duplication and will make factoring out parts common
with jbd2__journal_restart() easier.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191105164437.32602-14-jack@suse.cz


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