Update for alloc_buffer changes.

Update for alloc_buffer changes.

Original commit message from CVS:
2005-12-05  Andy Wingo  <wingo@pobox.com>

* ext/a52dec/gsta52dec.c: (gst_a52dec_push):
* ext/mad/gstmad.c: (gst_mad_chain):
* ext/mpeg2dec/gstmpeg2dec.c: (gst_mpeg2dec_alloc_buffer):
* gst/dvdlpcmdec/gstdvdlpcmdec.c: (gst_dvdlpcmdec_chain_raw):
* gst/iec958/ac3iec.c: (ac3iec_chain_raw):
* gst/realmedia/rmdemux.c: (gst_rmdemux_add_stream),
(gst_rmdemux_parse_packet): Update for alloc_buffer changes.