avcodec/jpeg2000dec: Use ff_set_dimensions()

Fixes: OOM
Fixes: 1890/clusterfuzz-testcase-minimized-6329019509243904

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