rc: suppress error on first package install, doesn't matter

src/etc/rc.configure_firmware

@@ -25,7 +25,11 @@
     CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     POSSIBILITY OF SUCH DAMAGE.
-*/
+ */
+
+if (!file_exists('/conf/config.xml')) {
+    exit(0);
+}
 
 require_once 'config.inc';
 require_once 'util.inc';