staging: unisys: visorbus: remove return values for write_vbus functions

This patch removes the return values from the write_vbus_* channel
functions. Nobody was checking the return values and the value stored
into the vbus info is not critical to the functioning of the device.

Signed-off-by: Erik Arfvidson <erik.arfvidson@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <Timothy.Sell@unisys.com>
Acked-By: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>