ocfs2: Fix setting of OCFS2_LOCK_BLOCKED during bast

During bast, set the OCFS2_LOCK_BLOCKED flag only if the lock needs to
downconverted.

Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Acked-by: Sunil Mushran <sunil.mushran@oracle.com>
Acked-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>