Introduce vm_get_vcpu helper function.

Change-Id: I46aef6d240a74357b96b6677d1ec4c8386076f57
diff --git a/src/cpu.c b/src/cpu.c
index 7a2ffe2..7d181dc 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -123,7 +123,7 @@
 
 	if (!prev) {
 		struct vm *vm = vm_get(HF_PRIMARY_VM_ID);
-		struct vcpu *vcpu = &vm->vcpus[cpu_index(c)];
+		struct vcpu *vcpu = vm_get_vcpu(vm, cpu_index(c));
 		struct vcpu_locked vcpu_locked;
 
 		vcpu_locked = vcpu_lock(vcpu);