staging: unisys: visornic: change return statements

Changes return statements in visornic_rx() to use literals instead of a
variable. Also changes function description to reflect the correct return
type.

Signed-off-by: David Binder <david.binder@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>