rpicamsrc: basesrc event handlers should not unref

Don't unref the passed event when handling events via
the GstBaseSrc src pad event handler - basesrc does
the unref. That breaks handling of upstream
force-key-unit events by unreffing twice.

Fixes https://github.com/thaytan/gst-rpicamsrc/issues/43

sys/rpicamsrc/gstrpicamsrc.c

@@ -1118,7 +1118,6 @@ gst_rpi_cam_src_event (GstBaseSrc * parent, GstEvent * event)
         } else {
           ret = FALSE;
         }
-        gst_event_unref (event);
       } else {
         ret = GST_BASE_SRC_CLASS (parent_class)->event (parent, event);
       }