riscv: use vma iterator for vdso

Remove the linked list use in favour of the vma iterator.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Alexandre Frade <kernel@xanmod.org>

arch/riscv/kernel/vdso.c

@@ -114,11 +114,12 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 {
 	struct mm_struct *mm = task->mm;
 	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
 	struct __vdso_info *vdso_info = mm->context.vdso_info;
 
 	mmap_read_lock(mm);
 
-	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+	for_each_vma(vmi, vma) {
 		unsigned long size = vma->vm_end - vma->vm_start;
 
 		if (vma_is_special_mapping(vma, vdso_info->dm))