Return non-zero exit status in case of error.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=547596

Based on Debian 04-fix_exit_code.patch .

--- macchanger-1.5.0/src/main.c.orig	2010-10-11 18:05:26.000000000 +0200
+++ macchanger-1.5.0/src/main.c	2010-10-11 18:25:54.000000000 +0200
@@ -115,6 +115,7 @@ main (int argc, char *argv[])
 	char       *device_name;
 
 	int val;
+	int ret = 1;
 
 	
 	/* Read the parameters */
@@ -221,6 +222,8 @@ main (int argc, char *argv[])
 		if (mc_mac_equal (mac, mac_faked)) {
 			printf ("It's the same MAC!!\n");
 		}
+
+		ret = 0;
 	}
 	
 	/* Memory free */
@@ -229,5 +232,5 @@ main (int argc, char *argv[])
 	mc_net_info_free (net);
 	mc_maclist_free();
 	
-	return 0;
+	return ret;
 }