media: atmel: atmel-isc: add HIS to register offsets

The HIS submodule is a part of the atmel-isc pipeline, and stands for
Histogram. This module performs a color histogram that can be read and used
by the main processor.
Add his to the reg offsets struct.
This will allow different products to have a different reg offset for this
particular module.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>