avcodec/diracdsp: fix integer overflow

Fixes: runtime error: signed integer overflow: 11 * 225726413 cannot be represented in type 'int'
Fixes: 2764/clusterfuzz-testcase-minimized-5382561922547712

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