Fix memory handle encoding.

We were sending handles as a single register in some cases, rather than
breaking them into two 32-bit registers as the FF-A spec requires.

Bug: 132420445
Change-Id: Ieb327ded2ad72f5332a1d001452176c8edbe0f08
diff --git a/src/ffa_memory.c b/src/ffa_memory.c
index 8def572..d31750d 100644
--- a/src/ffa_memory.c
+++ b/src/ffa_memory.c
@@ -1319,7 +1319,7 @@
 		return (struct ffa_value){.func = FFA_SUCCESS_32};
 	}
 
-	return (struct ffa_value){.func = FFA_SUCCESS_32, .arg2 = handle};
+	return ffa_mem_success(handle);
 }
 
 struct ffa_value ffa_memory_retrieve(struct vm_locked to_locked,