Removes error messages from "Recorded Programs" page

In Ubuntu 18.04, the following prints for lines
188 (and 189 for disk_used) on the above screen:

Warning at /var/www/mythweb/modules/tv/recorded.php, line 188:

!!NoTrans: Use of undefined constant disk_size - assumed 'disk_size' (this will throw an Error in a future version of PHP)!!

Author: Bill Meek

modules/tv/recorded.php

@@ -179,14 +179,14 @@
     if (function_exists('gmp_mul')) {
     // GMP functions should work better with 64 bit numbers.
         $size = gmp_mul('1024', $size);
-        define(disk_size, gmp_strval($size));
+        define('disk_size', gmp_strval($size));
         $size = gmp_mul('1024', $used);
-        define(disk_used, gmp_strval($size));
+        define('disk_used', gmp_strval($size));
     }
     else {
     // This is inaccurate, but it's the best we can get without GMP.
-        define(disk_size, ($size * 1024));
-        define(disk_used, ($used * 1024));
+        define('disk_size', ($size * 1024));
+        define('disk_used', ($used * 1024));
     }
 
 // Load the class for this page