xen/sched: address violation of MISRA C Rule 8.2

Rule 8.2 states: "Function types shall be in prototype form with
named parameters".

The parameter name is missing from the function pointer type
that constitutes the first parameter.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>

xen/common/sched/rt.c

@@ -500,7 +500,7 @@ deadline_queue_remove(struct list_head *queue, struct list_head *elem)
 }
 
 static inline bool
-deadline_queue_insert(struct rt_unit * (*qelem)(struct list_head *),
+deadline_queue_insert(struct rt_unit * (*qelem)(struct list_head *elem),
                       struct rt_unit *svc, struct list_head *elem,
                       struct list_head *queue)
 {