ide: don't BUG() on unsupported transfer modes

Fix ide-cris, cs5530, sc1200 and sis5513 host drivers to just return instead
of OOPS-ing for unsupported modes in ->set_dma_mode methods.
Acked-by: NSergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/cris/ide-cris.c

@@ -748,8 +748,7 @@ static void cris_set_dma_mode(ide_drive_t *drive, const u8 speed)
 			hold = ATA_DMA2_HOLD;
 			break;
 		default:
-			BUG();
-			break;
+			return;
 	}
 
 	if (speed >= XFER_UDMA_0)

drivers/ide/pci/cs5530.c

@@ -117,8 +117,7 @@ static void cs5530_set_dma_mode(ide_drive_t *drive, const u8 mode)
 		case XFER_MW_DMA_1:	timings = 0x00012121; break;
 		case XFER_MW_DMA_2:	timings = 0x00002020; break;
 		default:
-			BUG();
-			break;
+			return;
 	}
 	basereg = CS5530_BASEREG(drive->hwif);
 	reg = inl(basereg + 4);			/* get drive0 config register */

drivers/ide/pci/sc1200.c

@@ -186,8 +186,7 @@ static void sc1200_set_dma_mode(ide_drive_t *drive, const u8 mode)
 			}
 			break;
 		default:
-			BUG();
-			break;
+			return;
 	}
 
 	if (unit == 0) {			/* are we configuring drive0? */

drivers/ide/pci/sis5513.c

@@ -356,7 +356,6 @@ static void sis_set_dma_mode(ide_drive_t *drive, const u8 speed)
 			sis_program_timings(drive, speed);
 			break;
 		default:
-			BUG();
 			break;
 	}
 }