Introducing hf_vcpu_count_t for vCPU count.

Return 0 rather than -1 on error.

Change-Id: I95cdde0744ef13e9bd748ce8ed32439d3d7f2010
diff --git a/inc/hf/api.h b/inc/hf/api.h
index 4060075..43497bf 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -25,7 +25,8 @@
 void api_init(struct mpool *ppool);
 spci_vm_id_t api_vm_get_id(const struct vcpu *current);
 spci_vm_count_t api_vm_get_count(void);
-int64_t api_vcpu_get_count(spci_vm_id_t vm_id, const struct vcpu *current);
+spci_vcpu_count_t api_vcpu_get_count(spci_vm_id_t vm_id,
+				     const struct vcpu *current);
 void api_regs_state_saved(struct vcpu *vcpu);
 struct hf_vcpu_run_return api_vcpu_run(spci_vm_id_t vm_id,
 				       spci_vcpu_index_t vcpu_idx,