avcodec/cfhd: Fix undefined shift

Fixes: runtime error: left shift of negative value -1
Fixes: 2303/clusterfuzz-testcase-minimized-5529675273076736

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

libavcodec/cfhd.c

@@ -711,7 +711,7 @@ static int cfhd_decode(AVCodecContext *avctx, void *data, int *got_frame,
         output = s->plane[plane].subband[0];
         for (i = 0; i < lowpass_height * 2; i++) {
             for (j = 0; j < lowpass_width * 2; j++)
-                output[j] <<= 2;
+                output[j] *= 4;
 
             output += lowpass_width * 2;
         }