ext/ladspa/gstsignalprocessor.c: Make ladspa elements reusable. Fixes #350006.

ext/ladspa/gstsignalprocessor.c: Make ladspa elements reusable. Fixes #350006.

Original commit message from CVS:
Patch by: Andy Wingo <wingo at pobox dot com>
* ext/ladspa/gstsignalprocessor.c: (gst_signal_processor_setup),
(gst_signal_processor_start), (gst_signal_processor_stop),
(gst_signal_processor_cleanup), (gst_signal_processor_setcaps),
(gst_signal_processor_pen_buffer), (gst_signal_processor_flush),
(gst_signal_processor_do_pulls), (gst_signal_processor_do_pushes),
(gst_signal_processor_change_state):
Make ladspa elements reusable. Fixes #350006.