sbin/hammer: Minor cleanup

sbin/hammer: Minor cleanup

(zone-2 offset of layer1's big-block never changes once initialized)

  # grep "layer1_offset = " sys/vfs/hammer sbin/hammer -rI
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_blockmap.c:       layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_volume.c:         layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_volume.c:         layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_volume.c:         layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_volume.c:         layer1_offset = freemap->phys_offset +
  sys/vfs/hammer/hammer_volume.c:         layer1_offset = freemap->phys_offset +
  sbin/hammer/blockmap.c:         layer1_offset = freemap->phys_offset +
  sbin/hammer/blockmap.c: layer1_offset = freemap->phys_offset +
  sbin/hammer/blockmap.c: layer1_offset = freemap->phys_offset +
  sbin/hammer/ondisk.c:   layer1_offset = alloc_bigblock(root_vol, HAMMER_ZONE_FREEMAP_INDEX);
* sbin/hammer/ondisk.c:           layer1_offset = layer1_base +
* sbin/hammer/ondisk.c:           layer1_offset = layer1_base +
  sbin/hammer/cmd_blockmap.c:             layer1_offset = rootmap->phys_offset +