Re-constify pointer to current.

It doesn't actually get modified so can remain const.

Change-Id: I861a438b55a377496dc7794e25592fd5a02555c3
diff --git a/inc/hf/api.h b/inc/hf/api.h
index 2d956ef..06f33fd 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -27,7 +27,7 @@
 int64_t api_vm_get_count(void);
 int64_t api_vcpu_get_count(uint32_t vm_id, const struct vcpu *current);
 struct hf_vcpu_run_return api_vcpu_run(uint32_t vm_id, uint32_t vcpu_idx,
-				       struct vcpu *current,
+				       const struct vcpu *current,
 				       struct vcpu **next);
 int64_t api_vm_configure(ipaddr_t send, ipaddr_t recv, struct vcpu *current,
 			 struct vcpu **next);