ide: add ide_device_{get,put}() helpers

* Add 'struct ide_host *host' field to ide_hwif_t and set it
  in ide_host_alloc_all().

* Add ide_device_{get,put}() helpers loosely based on SCSI's
  scsi_device_{get,put}() ones.

* Convert IDE device drivers to use ide_device_{get,put}().

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/scsi/ide-scsi.c b/drivers/scsi/ide-scsi.c
index 5385524..318ef38 100644
--- a/drivers/scsi/ide-scsi.c
+++ b/drivers/scsi/ide-scsi.c
@@ -101,8 +101,13 @@
 
 	mutex_lock(&idescsi_ref_mutex);
 	scsi = ide_scsi_g(disk);
-	if (scsi)
+	if (scsi) {
 		scsi_host_get(scsi->host);
+		if (ide_device_get(scsi->drive)) {
+			scsi_host_put(scsi->host);
+			scsi = NULL;
+		}
+	}
 	mutex_unlock(&idescsi_ref_mutex);
 	return scsi;
 }
@@ -110,6 +115,7 @@
 static void ide_scsi_put(struct ide_scsi_obj *scsi)
 {
 	mutex_lock(&idescsi_ref_mutex);
+	ide_device_put(scsi->drive);
 	scsi_host_put(scsi->host);
 	mutex_unlock(&idescsi_ref_mutex);
 }