This patch is a first preparation of using the bdev mapping instead
of the JFS-private device mapping/inode for 2.4.1x/2.5:

 * add metapages to ->mp_list of the inode passed to __get_metapage
   instead of mp->mapping->host.  Do this outside of add_to_hash,
   and only do it for metapages that aren't mapped absolutely.
   RATIONALE: when using the bdev mapping, the absoloute inode won't
   have the JFS-private inode info.  It is save because we never
   traverse the mp_list of the direct inodes.
 * use a goto to unify two error handling pathes in __get_metapage.

Submitted by Christoph Hellwig