atp870u: Unify code format in is870(), is880() and is885()

Unify code formatting in is870(), is880() and is885() functions to simplify
comparing them.
Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>