afr: fix gapless playback with fatigue reduction enabled

afr_configure() returned 1 for every message. For
DSP_PROC_NEW_FORMAT that is PROC_NEW_FORMAT_DEACTIVATED, so the
DSP did not call the stage for the buffer that brought a new
format: the first buffer of each track went out unfiltered, and
the filters started on the second. That is 128 samples of a WAV
file, and the whole first block of a codec with 32-bit
non-interleaved output, 4608 samples of a FLAC file.

A codec sets the format again at the start of every track, so
between gapless tracks this put a short stretch of unfiltered
audio into filtered audio, heard as a click at the join.

Return 0, as the other stages do.

Found with test_codec's DSP checksums on a Sansa Clip+: a model
of the DSP with fatigue reduction left out of each file's first
buffer reproduces the sixteen checksums of two runs, and none of
them with it left in. Listening on the same player, the click
between gapless tracks is gone with this change.

Change-Id: I7a1193fa0a4ee0c983cbcc5c1af201e1678579d0
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/rbcodec/dsp/afr.c

@@ -137,7 +137,7 @@ static intptr_t afr_configure(struct dsp_proc_entry *this,
         break;
     }
 
-    return 1;
+    return 0;
 }
 
 /* Database entry */