staging: unisys: visorbus: Remove confusing comment in controlvmchannel.

Referencing a SegmentIndex doesn't make sense in the Linux drivers, get rid
of the comment.

Reviewed-by: Sameer Wadgaonkar <sameer.wadgaonkar@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>