bugfix: OTA Upgrade may mask backup errors.

During creation of the backup file some errors may be masked.

While this isn't confirmed to be the cause of any known report it
is possible users have in the past experienced this and we just
couldn't see it.

Change-Id: I12136b7c53aabfb243445170b91c69928206bb1b

files/www/cgi-bin/admin

@@ -249,7 +249,7 @@ if($fw_install and -f "$tmpdir/firmware")
             nvram_set("nodeupgraded","1");
             
             system("tar -czf /tmp/arednsysupgradebackup.tgz -T /tmp/sysupgradefilelist");
-            if ($? == 1) {
+            if ($? != 0) {
                 print "
 <center><h2>ERROR: Could not backup filesystem.</h2>
 <h3>An error occured trying to backup the file system. Node will now reboot.