[S390] subchannel register/unregister mutex.

Add a reg_mutex to prevent unregistering a subchannel before it has been
registered. Since 2.6.17, we've seen oopses in kslowcrw when a device is
found to be not operational during sense id when doing initial device
recognition; it is not clear yet why that particular problem was not (yet)
observed with earlier kernels...

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index 67f0de6..9db0987 100644
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -280,7 +280,7 @@
 	 * 'throw away device'.
 	 */
 	sch = to_subchannel(cdev->dev.parent);
-	device_unregister(&sch->dev);
+	css_sch_device_unregister(sch);
 	/* Reset intparm to zeroes. */
 	sch->schib.pmcw.intparm = 0;
 	cio_modify(sch);
@@ -625,7 +625,7 @@
 					other_sch->schib.pmcw.intparm = 0;
 					cio_modify(other_sch);
 				}
-				device_unregister(&other_sch->dev);
+				css_sch_device_unregister(other_sch);
 			}
 		}
 		/* Update ssd info here. */
@@ -709,7 +709,7 @@
 	struct subchannel *sch;
 
 	sch = to_subchannel(cdev->dev.parent);
-	device_unregister(&sch->dev);
+	css_sch_device_unregister(sch);
 	/* Reset intparm to zeroes. */
 	sch->schib.pmcw.intparm = 0;
 	cio_modify(sch);