Retrieve channel count from gm20b specific header instead of the
gk20a header. This increases channel count from 128 to 512.
Change-Id: I96d4887432852795f7f526e33f0d3d2458f3af0e
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/500623