ide: remove drive->ctl

Remove drive->ctl (it is always equal to 0x08 after init time).

While at it:

* Use ATA_DEVCTL_OBS define.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/pci/sgiioc4.c b/drivers/ide/pci/sgiioc4.c
index c1b667c..24513e3d 100644
--- a/drivers/ide/pci/sgiioc4.c
+++ b/drivers/ide/pci/sgiioc4.c
@@ -111,7 +111,7 @@
 static void
 sgiioc4_maskproc(ide_drive_t * drive, int mask)
 {
-	writeb(mask ? (drive->ctl | 2) : (drive->ctl & ~2),
+	writeb(ATA_DEVCTL_OBS | (mask ? 2 : 0),
 	       (void __iomem *)drive->hwif->io_ports.ctl_addr);
 }