ide: add ide_set_dma() helper (v2)

* add ide_set_dma() helper and make ide_hwif_t.ide_dma_check return
  -1 when DMA needs to be disabled (== need to call ->ide_dma_off_quietly)
   0 when DMA needs to be enabled  (== need to call ->ide_dma_on)
   1 when DMA setting shouldn't be changed
* fix IDE code to use ide_set_dma() instead if using ->ide_dma_check directly

v2:
* updated for scc_pata

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

diff --git a/drivers/ide/ide-probe.c b/drivers/ide/ide-probe.c
index 176bbc8..72218f3 100644
--- a/drivers/ide/ide-probe.c
+++ b/drivers/ide/ide-probe.c
@@ -857,7 +857,7 @@
 #ifdef CONFIG_IDEDMA_ONLYDISK
 				if (drive->media == ide_disk)
 #endif
-					hwif->ide_dma_check(drive);
+					ide_set_dma(drive);
 			}
 		}
 	}