jbd: Revise KERN_EMERG error messages

Some of KERN_EMERG printk messages do not really deserve this log level
and the one in log_wait_commit() is even rather useless (the journal has
been previously aborted and *that* is where we should have been
complaining). So make some messages just KERN_ERR and remove the useless
message.

Signed-off-by: Jan Kara <jack@suse.cz>