gst/base/gstbasesrc.c: Don't unref the caps we passed to gst_caps_make_writable() after passing them. gst_caps_make_w...

Original commit message from CVS:
* gst/base/gstbasesrc.c: (gst_base_src_default_negotiate):
Don't unref the caps we passed to gst_caps_make_writable() after
passing them. gst_caps_make_writable() will do that for us.