Remove practice of assigning random const pointers to device id.

This is not required as cache code already checks driver id as well.

grub-core/fs/cbfs.c

@@ -291,7 +291,7 @@ grub_cbfsdisk_open (const char *name, grub_disk_t disk)
 
   disk->total_sectors = cbfsdisk_size / GRUB_DISK_SECTOR_SIZE;
   disk->max_agglomerate = GRUB_DISK_MAX_MAX_AGGLOMERATE;
-  disk->id = (unsigned long) "cbfs";
+  disk->id = 0;
 
   return GRUB_ERR_NONE;
 }