tests/datawizard/variable_size.c: do not use keywords as variable name

(cherry picked from commit 0da5163a0f26ff116bf7c31b60cf244f0bbf31da)

tests/datawizard/variable_size.c

@@ -100,7 +100,7 @@ void variable_size_data_register(starpu_data_handle_t *handleptr, unsigned x, un
 	/* Simulate that tiles close to the diagonal are more dense */
 	vsinterface.size = FULLSIZE * (starpu_lrand48() % 1024 + 1024) / 2048. * (N-sqrt(abs((int)x-(int)y)*N)) / N;
 	/* Round to page size */
-	vsinterface.size -= interface.size & (65536-1);
+	vsinterface.size -= vsinterface.size & (65536-1);
 
 	_starpu_simgrid_data_new(vsinterface.size);