Btrfs: don't use ram_bytes for uncompressed inline items

Btrfs: don't use ram_bytes for uncompressed inline items

commit 514ac8ad8793a097c0c9d89202c642479d6dfa34 upstream.

If we truncate an uncompressed inline item, ram_bytes isn't updated to reflect
the new size.  The fixe uses the size directly from the item header when
reading uncompressed inlines, and also fixes truncate to update the
size as it goes.

Reported-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
[bwh: Backported to 3.2:
 - Don't use btrfs_map_token API
 - There are fewer callers of btrfs_file_extent_inline_len() to change
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>