Revert "rtpjitterbuffer: don't forget to unlock mutex in error code path in two cases"

This reverts commit a7fb7b53592d87f7983544debb74d364fc3257ad.

The mutex is taken by the caller, we should keep it locked when returning so
the caller can unlock it again.

gst/rtpmanager/gstrtpjitterbuffer.c

@@ -1730,7 +1730,6 @@ no_caps:
   }
 out_flushing:
   {
-    JBUF_UNLOCK (jitterbuffer->priv);
     GST_DEBUG_OBJECT (jitterbuffer, "we are flushing");
     return GST_FLOW_FLUSHING;
   }
@@ -3052,7 +3051,6 @@ pop_and_push_next (GstRtpJitterBuffer * jitterbuffer, guint seqnum)
   /* ERRORS */
 out_flushing:
   {
-    JBUF_UNLOCK (priv);
     return priv->srcresult;
   }
 }