slc90e66: carry over fixes from piix driver

slc90e66: carry over fixes from piix driver

Synchronize with version 0.46 of the Intel PIIX/ICH driver:

- carry over Alan's and my own fixes in the tuneproc() method and my cleanups
  both there and in the ratemask() method;

- SLC90E66 only supports MW DMA modes 1/2 and SW DMA mode 2 (just like Intel
  chips), so don't claim support for other MW/SW DMA modes;

- don't check dor non-NULL drive->id in the ide_dma_check() method -- this is
  assumed to be true in all other drivers;

- do some coding/formatting cleanups while at it...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>