staging: unisys: removed unused channel_bytes attribute

The channel_bytes attribute in the visor_device struct was meant to keep
track of the number of bytes in the associated channel of the device.
Not only is the variable never set nor used, but the information can
already be accessed by referencing visor_device->visorchannel->nbytes.

Signed-off-by: Alexander Curtin <alexander.curtin@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>