ide: make ide_unregister() take 'ide_hwif_t *' as an argument (take 2)

* Make ide_unregister() take 'ide_hwif_t *hwif' instead of 'unsigned int
  index' (hwif->index) as an argument and update all users accordingly.

While at it:

* Remove unnecessary checks for hwif != NULL from ide-pnp.c::idepnp_remove()
  and delkin_cb.c::delkin_cb_remove().

* Remove needless hwif->chipset assignment from scc_pata.c::scc_remove().

v2:
* Fixup ide_unregister() documentation.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/pci/scc_pata.c b/drivers/ide/pci/scc_pata.c
index 17cf864..f80306b 100644
--- a/drivers/ide/pci/scc_pata.c
+++ b/drivers/ide/pci/scc_pata.c
@@ -763,9 +763,8 @@
 		hwif->dmatable_cpu = NULL;
 	}
 
-	ide_unregister(hwif->index);
+	ide_unregister(hwif);
 
-	hwif->chipset = ide_unknown;
 	iounmap((void*)ports->dma);
 	iounmap((void*)ports->ctl);
 	pci_release_selected_regions(dev, (1 << 2) - 1);