jbd: relocate assert after state lock in journal_commit_transaction()

The state lock is taken after we are doing an assert on the state
value, not before.  So we might in fact be doing an assert on a
transient value.  Ensure the state check is within the scope of
the state lock being taken.

Backport of jbd2 commit 3ca841c1
("jbd2: relocate assert after state lock in journal_commit_transaction()")

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jan Kara <jack@suse.cz>