GenWQE: Fix problem when reading HSI and Retc

This patch fixes a problem we found during debug on PPC64 when
reading HSI status and Retc.

Signed-off-by: Eberhard S. Amann <esa@linux.vnet.ibm.com>
Signed-off-by: Frank Haverkamp <haver@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/genwqe/card_ddcb.c

@@ -390,8 +390,9 @@ static int genwqe_check_ddcb_queue(struct genwqe_dev *cd,
 		    0x00000000)
 			goto go_home; /* not completed, continue waiting */
 
-		/* Note: DDCB could be purged */
+		wmb();  /*  Add sync to decouple prev. read operations */
 
+		/* Note: DDCB could be purged */
 		req = queue->ddcb_req[queue->ddcb_act];
 		if (req == NULL) {
 			/* this occurs if DDCB is purged, not an error */