[PATCH] libata: convert @post_reset to @flags in ata_dev_read_id()

Make ata_dev_read_id() take @flags instead of @post_reset.  Currently
there is only one flag defined - ATA_READID_POSTRESET, which is
equivalent to @post_reset.  This is preparation for polling presence
detection.

Signed-off-by: Jeff Garzik <jeff@garzik.org>