max: fix format

src/drivers/max/driver_fpga.c

@@ -201,7 +201,7 @@ static void init_device_context(unsigned devid)
 			{
 				char *colon = strstr(load->engine_id_pattern, ":*");
 				snprintf(s, sizeof(s), "%.*s:%u",
-						colon - load->engine_id_pattern,
+						(int) (colon - load->engine_id_pattern),
 						load->engine_id_pattern,
 						(unsigned) devid);
 			}