Move ide_find_port() call to pmac_ide_setup_device().

While at it:

- fix return value (s/-ENODEV/-ENOENT/)

- add DRV_NAME define and use it to set name field of pmac_port_info

- use ide_find_port_slot() instead of ide_find_port()

- remove superfluous error message (ide_find_port_slot() takes care of it)

- drop IDE interface number from driver banner message (but include bus type)

v2:
* Build fix (thanks to Stephen Rothwell for noticing the issue).

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>