[S390] cio: Make ccw_dev_id_is_equal() more robust.

Using memcmp to compare ccw_dev_id implies that the whole structure (incl.
padding) has always been completely initialized to sane values. Comparing
the structures field by field doesn't make such assumptions.
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

include/asm-s390/cio.h

@@ -278,7 +278,10 @@ struct ccw_dev_id {
 static inline int ccw_dev_id_is_equal(struct ccw_dev_id *dev_id1,
 				      struct ccw_dev_id *dev_id2)
 {
-	return !memcmp(dev_id1, dev_id2, sizeof(struct ccw_dev_id));
+	if ((dev_id1->ssid == dev_id2->ssid) &&
+	    (dev_id1->devno == dev_id2->devno))
+		return 1;
+	return 0;
 }
 
 extern int diag210(struct diag210 *addr);