Fix 'pointers are not permitted as case values' compile error.

dlls/user/dde/server.c

diff --git a/dlls/user/dde/server.c b/dlls/user/dde/server.c
index ada9349..c90c6a4 100644
--- a/dlls/user/dde/server.c
+++ b/dlls/user/dde/server.c
@@ -577,7 +577,7 @@
 	WDML_PostAck(pConv, WDML_SERVER_SIDE, 0, FALSE, FALSE, pXAct->atom,
                      pXAct->lParam, WM_DDE_REQUEST);
 	break;
-    case CBR_BLOCK:
+    case (ULONG_PTR)CBR_BLOCK:
 	ret = WDML_QS_BLOCK;
 	break;
     default: