cashew: fix NDEBUG build failure

DCHECK_NOTNULL(foo) produces a "statement has no effect" error during
NDEBUG compilation, while DCHECK(foo != NULL) does not.

BUG=chromium-os:8800
TEST=USE=-cros-debug emerge-<board> cashew

Change-Id: I6e62d0e2f90f1412cd2d252a11e73623c308178d

TBR=djkurtz@chromium.org

src/data_plan.cc

diff --git a/src/data_plan.cc b/src/data_plan.cc
index ca58fb3..19916d2 100644
--- a/src/data_plan.cc
+++ b/src/data_plan.cc
@@ -306,7 +306,7 @@
   DataPlanList::const_iterator it;
   for (it = data_plans.begin(); it != data_plans.end(); ++it) {
     DataPlan *plan = *it;
-    DCHECK_NOTNULL(plan);
+    DCHECK(plan != NULL);
     if (plan->IsActive()) {
       return plan;
     }