Convert direct reads of an inode's i_size to using i_size_read().
i_size_{read,write} use a seqcount to protect reads from accessing
incomple writes. Concurrent i_size_write()s require mutual exclussion
to protect the seqcount that is used by i_size_{read,write}. But
i_size_read() callers do not need to use additional locking.
Signed-off-by: Mike Snitzer <snitzer@redhat.com> Acked-by: NeilBrown <neilb@suse.de> Acked-by: Lars Ellenberg <lars.ellenberg@linbit.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>