ide-generic: add missing hwif->chipset setup

hwif->chipset need to be set properly or ide-generic driver will break once
we make a final step in fixing host drivers' dependence on ide_hwifs[].

Problem was catched early thanks to IDE tree exposure in -mm / -next trees
and reported by people listed people (thank you guys!).

Reported-by: "John Keller" <jpk@sgi.com>
Reported-by: Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
Reported-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>