btrfs: rework end io for extent buffer reads

Now that the only thing that keeps eb's alive is io_pages and it's
refcount we need to hold the eb ref for the entire end io call so we
don't get it removed out from underneath us.  Also the hooks make no
sense for us now, so rework this to be cleaner.

Signed-off-by: Josef Bacik <jbacik@fb.com>
3 files changed