libata: add @ap to ata_wait_register() and introduce ata_msleep()

Add optional @ap argument to ata_wait_register() and replace msleep()
calls with ata_msleep() which take optional @ap in addition to the
duration.  These will be used to implement EH exclusion.

This patch doesn't cause any behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 06a4db1..6780f4d 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -779,7 +779,7 @@
 
 	/* make sure SCSI EH is complete */
 	if (scsi_host_in_recovery(ap->scsi_host)) {
-		msleep(10);
+		ata_msleep(ap, 10);
 		goto retry;
 	}
 }