avcodec/alsdec: Avoid 1 layer of pointer dereferences in INTERLEAVE_OUTPUT()

This optimizes the code slightly (116 -> 80sec)
Testcase: 18668/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5710836719157248
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/alsdec.c

@@ -1819,16 +1819,17 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame_ptr,
     {                                                                                \
         int##bps##_t *dest = (int##bps##_t*)frame->data[0];                          \
         int channels = avctx->channels;                                              \
-        int32_t **raw_samples = ctx->raw_samples;                                    \
+        int32_t *raw_samples = ctx->raw_samples[0];                                  \
+        int raw_step = channels > 1 ? ctx->raw_samples[1] - raw_samples : 1;         \
         shift = bps - ctx->avctx->bits_per_raw_sample;                               \
         if (!ctx->cs_switch) {                                                       \
             for (sample = 0; sample < ctx->cur_frame_length; sample++)               \
                 for (c = 0; c < channels; c++)                                       \
-                    *dest++ = raw_samples[c][sample] * (1U << shift);                \
+                    *dest++ = raw_samples[c*raw_step + sample] * (1U << shift);      \
         } else {                                                                     \
             for (sample = 0; sample < ctx->cur_frame_length; sample++)               \
                 for (c = 0; c < channels; c++)                                       \
-                    *dest++ = raw_samples[sconf->chan_pos[c]][sample] * (1U << shift);\
+                    *dest++ = raw_samples[sconf->chan_pos[c]*raw_step + sample] * (1U << shift);\
         }                                                                            \
     }