Rename manifest.num_vms to vm_count

Rename variable to conform to Hafnium's style guide.

Change-Id: I0b983c98eb28195bc23ba4947857d0d63a990ae3
diff --git a/inc/hf/manifest.h b/inc/hf/manifest.h
index 46bd205..57657c7 100644
--- a/inc/hf/manifest.h
+++ b/inc/hf/manifest.h
@@ -44,7 +44,7 @@
  * Hafnium manifest parsed from FDT.
  */
 struct manifest {
-	spci_vm_count_t num_vms;
+	spci_vm_count_t vm_count;
 	struct manifest_vm vm[MAX_VMS];
 };