x86/smp: address a violation of MISRA C:2012 Rule 8.2

Add missing parameter name. No functional change.

Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/include/asm/smp.h

@@ -32,7 +32,7 @@ extern bool park_offline_cpus;
 
 void smp_send_nmi_allbutself(void);
 
-void send_IPI_mask(const cpumask_t *, int vector);
+void send_IPI_mask(const cpumask_t *mask, int vector);
 void send_IPI_self(int vector);
 
 extern void (*mtrr_hook) (void);