irqbypass: Disallow NULL token

A NULL token is meaningless and can only lead to unintended problems.
Error on registration with a NULL token, ignore de-registrations with
a NULL token.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/include/linux/irqbypass.h b/include/linux/irqbypass.h
index 1551b5b..f0f5d26 100644
--- a/include/linux/irqbypass.h
+++ b/include/linux/irqbypass.h
@@ -34,7 +34,7 @@
 /**
  * struct irq_bypass_producer - IRQ bypass producer definition
  * @node: IRQ bypass manager private list management
- * @token: opaque token to match between producer and consumer
+ * @token: opaque token to match between producer and consumer (non-NULL)
  * @irq: Linux IRQ number for the producer device
  * @add_consumer: Connect the IRQ producer to an IRQ consumer (optional)
  * @del_consumer: Disconnect the IRQ producer from an IRQ consumer (optional)
@@ -60,7 +60,7 @@
 /**
  * struct irq_bypass_consumer - IRQ bypass consumer definition
  * @node: IRQ bypass manager private list management
- * @token: opaque token to match between producer and consumer
+ * @token: opaque token to match between producer and consumer (non-NULL)
  * @add_producer: Connect the IRQ consumer to an IRQ producer
  * @del_producer: Disconnect the IRQ consumer from an IRQ producer
  * @stop: Perform any quiesce operations necessary prior to add/del (optional)