a_read_native_max_address()
and combine ata_set_native_max_address_ext() and
ata_set_native_max_address() into ata_set_max_sectors().

* reduce duplicate code
* return 0 or -errno depending on error conditions
* report if command fails
* use ATA_LBA instead of 0x40

This is in preparation of ata_hpa_resize() update.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
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