xen/notifier: address violations of MISRA C:2012 Rule 8.2

Add missing parameter names. No functional change.

Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/include/xen/notifier.h

@@ -23,7 +23,8 @@
  */
 
 struct notifier_block {
-    int (*notifier_call)(struct notifier_block *, unsigned long, void *);
+    int (*notifier_call)(struct notifier_block *nfb, unsigned long action,
+                         void *hcpu);
     struct list_head chain;
     int priority;
 };