avcodec/dss_sp: Fix multiple left shift of negative value -466

Fixes: 1339/clusterfuzz-testcase-minimized-4614671485108224

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

libavcodec/dss_sp.c

@@ -33,7 +33,7 @@
 
 #define DSS_SP_FRAME_SIZE        42
 #define DSS_SP_SAMPLE_COUNT     (66 * SUBFRAMES)
-#define DSS_SP_FORMULA(a, b, c) (((((a) << 15) + (b) * (c)) + 0x4000) >> 15)
+#define DSS_SP_FORMULA(a, b, c) (((((a) * (1 << 15)) + (b) * (c)) + 0x4000) >> 15)
 
 typedef struct DssSpSubframe {
     int16_t gain;
@@ -499,7 +499,7 @@ static void dss_sp_scale_vector(int32_t *vec, int bits, int size)
             vec[i] = vec[i] >> -bits;
     else
         for (i = 0; i < size; i++)
-            vec[i] = vec[i] << bits;
+            vec[i] = vec[i] * (1 << bits);
 }
 
 static void dss_sp_update_buf(int32_t *hist, int32_t *vector)