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/mips/au1xxx-ide.c b/drivers/ide/mips/au1xxx-ide.c
index 3485a31..0f63994 100644
--- a/drivers/ide/mips/au1xxx-ide.c
+++ b/drivers/ide/mips/au1xxx-ide.c
@@ -627,7 +627,7 @@
 	ide_hwif_t *hwif = dev_get_drvdata(dev);
 	_auide_hwif *ahwif = &auide_hwif;
 
-	ide_unregister(hwif->index);
+	ide_unregister(hwif);
 
 	iounmap((void *)ahwif->regbase);