[PATCH] libata: update ata_dev_init_params()

Update ata_dev_init_params() such that it doesn't disable port
directly but return with appropriate error mask on failure.  This is
preparation for splitting ata_dev_identify().  Note that this patch
changes behavior of dev_init_params failure such that only failing
devices are taken offline not the whole port.  This change is
intended.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>