ide: use __generic_unplug_device() in ide_do_drive_cmd() (take 2)

* Call __elv_add_request() with 'plug' == 1 (so the device will be
  plugged) and then use __generic_unplug_device() instead of calling
  ide_do_request() directly.

v2:
* For blk_pm_resume_request() requests the queue is stopped so we
  need to call ->request_fn explicitly.

  Thanks to:
  - Rafael for reporting/bisecting the bug
  - Borislav/Rafael for testing the fix

This is a preparation for converting IDE to use blk_execute_rq().

Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Borislav Petkov <petkovbb@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-io.c

@@ -1606,8 +1606,11 @@ int ide_do_drive_cmd (ide_drive_t *drive, struct request *rq, ide_action_t actio
 	spin_lock_irqsave(&ide_lock, flags);
 	if (action == ide_preempt)
 		hwgroup->rq = NULL;
-	__elv_add_request(drive->queue, rq, where, 0);
-	ide_do_request(hwgroup, IDE_NO_IRQ);
+	__elv_add_request(drive->queue, rq, where, 1);
+	__generic_unplug_device(drive->queue);
+	/* the queue is stopped so it won't be plugged+unplugged */
+	if (blk_pm_resume_request(rq))
+		do_ide_request(drive->queue);
 	spin_unlock_irqrestore(&ide_lock, flags);
 
 	err = 0;