clock: Return FALSE in all paths that don't set out parameters in gst_clock_add_observation_unapplied()

It returned TRUE when regression failed, while not setting any of the out
parameters. This caused uninitialized data from the stack to be used for
setting the clock calibration.

gst/gstclock.c

@@ -1474,7 +1474,7 @@ invalid:
   {
     /* no valid regression has been done, ignore the result then */
     GST_CLOCK_SLAVE_UNLOCK (clock);
-    return TRUE;
+    return FALSE;
   }
 }