xen: make xen_flush_tlb_all() static

xen_flush_tlb_all() is used in arch/x86/xen/mmu.c only. Make it static.
Signed-off-by: NJuergen Gross <jgross@suse.com>
Reviewed-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>

arch/x86/xen/mmu.c

@@ -42,7 +42,7 @@ xmaddr_t arbitrary_virt_to_machine(void *vaddr)
 }
 EXPORT_SYMBOL_GPL(arbitrary_virt_to_machine);
 
-void xen_flush_tlb_all(void)
+static void xen_flush_tlb_all(void)
 {
 	struct mmuext_op *op;
 	struct multicall_space mcs;