[PATCH] ata: fix platform_device_register_simple() error check

The return value of platform_device_register_simple() should be checked
by IS_ERR().

Cc: Jeff Garzik <jgarzik@pobox.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>