Correct some broken printf() like format mismatches

Fix two places where a printf()-style format string does not match the
arguments passed.

Reported-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

dtc.c

@@ -216,7 +216,7 @@ int main(int argc, char *argv[])
 			alignsize = strtol(optarg, NULL, 0);
 			if (!is_power_of_2(alignsize))
 				die("Invalid argument \"%d\" to -a option\n",
-				    optarg);
+				    alignsize);
 			break;
 		case 'f':
 			force = true;