staging: unisys: visorchipset change -1 return value

This patch changes the vague -1 return value to -EINVAL

Signed-off-by: Erik Arfvidson <erik.arfvidson@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>