r600: update vport z & clipping when depth_clamp is changed

fixes piglit depth_clamp
diff --git a/src/mesa/drivers/dri/r600/r700_state.c b/src/mesa/drivers/dri/r600/r700_state.c
index 3c8cb57..a795f62 100644
--- a/src/mesa/drivers/dri/r600/r700_state.c
+++ b/src/mesa/drivers/dri/r600/r700_state.c
@@ -59,6 +59,7 @@
 static void r700UpdatePolygonMode(GLcontext * ctx);
 static void r700SetPolygonOffsetState(GLcontext * ctx, GLboolean state);
 static void r700SetStencilState(GLcontext * ctx, GLboolean state);
+static void r700UpdateWindow(GLcontext * ctx, int id);
 
 void r700UpdateShaders(GLcontext * ctx)
 {
@@ -780,6 +781,9 @@
 	case GL_LINE_STIPPLE:
 		r700UpdateLineStipple(ctx);
 		break;
+	case GL_DEPTH_CLAMP:
+		r700UpdateWindow(ctx, 0);
+		break;
 	default:
 		break;
 	}