ceph: allow xlock state to be LOCK_PREXLOCK when putting it

When the journal logs are successfully flushed the lockers' state
could be LOCK_PREXLOCK if the inflight OP need to gather issued
caps.

Fixes: https://tracker.ceph.com/issues/44565
Signed-off-by: Xiubo Li <xiubli@redhat.com>

src/mds/SimpleLock.h

@@ -417,6 +417,7 @@ class SimpleLock {
     ceph_assert(state == LOCK_XLOCK || state == LOCK_XLOCKDONE ||
 	   state == LOCK_XLOCKSNAP || state == LOCK_LOCK_XLOCK ||
 	   state == LOCK_LOCK  || /* if we are a leader of a peer */
+	   state == LOCK_PREXLOCK ||
 	   is_locallock());
     --more()->num_xlock;
     parent->put(MDSCacheObject::PIN_LOCK);