ocfs2: Update atime in splice read if necessary.

We should call ocfs2_inode_lock_atime instead of ocfs2_inode_lock
in ocfs2_file_splice_read like we do in ocfs2_file_aio_read so
that we can update atime in splice read if necessary.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>