[PATCH] libata: ignore CFA signature while sanity-checking an ATAPI device

0x848a in ID word 0 indicates CFA device iff the ID data is obtained from
IDENTIFY DEVICE.  For ATAPI devices, 0x848a in ID work 0 indicates valid
ATAPI device.  Fix sanity check in ata_dev_read_id() such that ATAPI
devices reporting 0x848a in ID word 0 is not handled as error.

The problem is identified by J.A.  Magallon with HL-DT-ST DVDRAM GSA-4120B.

Signed-off-by: Tejun Helo <htejun@gmail.com>
Cc: J.A. Magallon <jamagallon@ono.com>
Acked-by: Jeff Garzik <jeff@garzik.org>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>