aggregator: Reset the pad's first buffer flag with the rest

There is not reason to have separate code to reset this one.

https://bugzilla.gnome.org/show_bug.cgi?id=781673
diff --git a/libs/gst/base/gstaggregator.c b/libs/gst/base/gstaggregator.c
index 9a688dc..14bef99 100644
--- a/libs/gst/base/gstaggregator.c
+++ b/libs/gst/base/gstaggregator.c
@@ -245,6 +245,7 @@
   aggpad->priv->head_time = GST_CLOCK_TIME_NONE;
   aggpad->priv->tail_time = GST_CLOCK_TIME_NONE;
   aggpad->priv->time_level = 0;
+  aggpad->priv->first_buffer = TRUE;
 }
 
 static gboolean
@@ -1096,8 +1097,6 @@
         GST_OBJECT_UNLOCK (self);
       }
 
-      aggpad->priv->first_buffer = TRUE;
-
       /* We never forward the event */
       goto eat;
     }
@@ -2464,7 +2463,6 @@
   g_mutex_init (&pad->priv->flush_lock);
   g_mutex_init (&pad->priv->lock);
 
-  pad->priv->first_buffer = TRUE;
   gst_aggregator_pad_reset_unlocked (pad);
 }