staging: unisys: Add a function to set the clientpartition

This patch is an attempt to help hide the channel info behind
accessory functions.  I was trying to keep visorchannel as private
as possible.

The only function missing that seemed to be needed for now was
the ability to set the clientpartition.  So I expose that here.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>