avcodec/mlpdsp: Fix undefined shift ff_mlp_pack_output()

Fixes: runtime error: left shift of negative value -7862264
Fixes: 4074/clusterfuzz-testcase-minimized-4516104123711488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mlpdsp.c

@@ -117,7 +117,7 @@ int32_t ff_mlp_pack_output(int32_t lossless_check_data,
                           (1U << output_shift[mat_ch]);
             lossless_check_data ^= (sample & 0xffffff) << mat_ch;
             if (is32)
-                *data_32++ = sample << 8;
+                *data_32++ = sample * 256;
             else
                 *data_16++ = sample >> 8;
         }