This fixes pixel values not being properly shifted in
libopenjpeg_copyto16 and libopenjpeg_copy_to_packed16 methods.

Pixel formats like xyz12le need to be shifted by AVComponentDescriptor::shift
to get the correct values.
Reviewed-by: Michael Bradshaw <mjbshaw@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>