gst/gstvalue.*: Drop leading '%' from GST_FOURCC_FORMAT, thus making it consistent with our other format defines (#32...

Original commit message from CVS:
* gst/gstvalue.c: (gst_value_transform_fourcc_string),
(gst_value_serialize_fourcc):
* gst/gstvalue.h:
Drop leading '%' from GST_FOURCC_FORMAT, thus making it
consistent with our other format defines (#320324).