when rom file is too big, mention how many bytes

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@5046 a1c6a512-1295-4272-9138-f99709370657

tools/romsizetest.pl

@@ -27,6 +27,6 @@ my $max = $romsize - $romstart;
 my $file = filesize($ARGV[1]);
 
 if($file > $max ) {
-    print "Output is larger than max ($max)\n";
+    printf "Output is %d bytes larger than max ($max)\n", $file-$max;
     exit 1;
 }