sgi-xpc: Remove NULL pointer dereference.

If the bte copy fails, the attempt to retrieve payloads merely returns a
null pointer deref and not NULL as was expected.
Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Dean Nelson <dcn@sgi.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/sgi-xp/xpc_sn2.c

@@ -1957,11 +1957,13 @@ xpc_get_deliverable_payload_sn2(struct xpc_channel *ch)
 
 			msg = xpc_pull_remote_msg_sn2(ch, get);
 
-			DBUG_ON(msg != NULL && msg->number != get);
-			DBUG_ON(msg != NULL && (msg->flags & XPC_M_SN2_DONE));
-			DBUG_ON(msg != NULL && !(msg->flags & XPC_M_SN2_READY));
+			if (msg != NULL) {
+				DBUG_ON(msg->number != get);
+				DBUG_ON(msg->flags & XPC_M_SN2_DONE);
+				DBUG_ON(!(msg->flags & XPC_M_SN2_READY));
 
-			payload = &msg->payload;
+				payload = &msg->payload;
+			}
 			break;
 		}