10- and 12-bit DNxHR use the same DC coefficient decoding process and
VLC table, just with a different shift value. From SMPTE 2019-1:2016,
8.2.4 DC Coefficient Decoding:

"For 8-bit video sampling, the maximum value of η=11 and for
10-/12-bit video sampling, the maximum value of η=13."

A sample file will be uploaded to show that with this patch, things
decode correctly:
dnxhr_hqx_12bit_1080p_smpte_colorbars_davinci_resolve.mov
Signed-off-by: Steven Robertson <steven@strobe.cc>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>