ide: make ide_hwif_t.ide_dma_host_on void (v2)

* since ide_hwif_t.ide_dma_host_on is called either when drive->using_dma == 1
  or when return value is discarded make it void, also drop "ide_" prefix
* make __ide_dma_host_on() void and drop "__" prefix

v2:
* while at it rename atiixp_ide_dma_host_on() to atiixp_dma_host_on()
  and sgiioc4_ide_dma_host_on() to sgiioc4_dma_host_on().
  [ Noticed by Sergei Shtylyov <sshtylyov@ru.mvista.com>. ]

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>