sim: return from cpin when sim ready for telit

Especially for Telit HE910 it is not enough to wait for
entering a PIN code.
If we do not wait for #QSS: 3, subsequent commands,
like +CMER will report SIM BUSY and the network registration
atom will be removed as a consequence.

drivers/atmodem/sim.c

@@ -1178,7 +1178,7 @@ static void at_qss_notify(GAtResult *result, gpointer user_data)
 		return;
 
 	switch (state) {
-	case 2:	/* PIN unlocked */
+	case 3:	/* SIM inserted and READY. */
 		break;
 	default:
 		return;