shill: cellular: Replace NULL with nullptr.

BUG=None
TEST=`USE=cellular FEATURES=test emerge-$BOARD shill`

Change-Id: I5b4fc9d5326a18aaac8e26b13335cb665e18ee7c
Reviewed-on: https://chromium-review.googlesource.com/220653
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
diff --git a/cellular_capability_cdma.cc b/cellular_capability_cdma.cc
index 8fb6666..a7f01e5 100644
--- a/cellular_capability_cdma.cc
+++ b/cellular_capability_cdma.cc
@@ -307,7 +307,7 @@
   SignalQualityCallback callback =
       Bind(&CellularCapabilityCDMA::OnGetSignalQualityReply,
            weak_ptr_factory_.GetWeakPtr());
-  proxy_->GetSignalQuality(NULL, callback, kTimeoutDefault);
+  proxy_->GetSignalQuality(nullptr, callback, kTimeoutDefault);
 }
 
 void CellularCapabilityCDMA::GetRegistrationState() {
@@ -315,7 +315,7 @@
   RegistrationStateCallback callback =
       Bind(&CellularCapabilityCDMA::OnGetRegistrationStateReply,
            weak_ptr_factory_.GetWeakPtr());
-  proxy_->GetRegistrationState(NULL, callback, kTimeoutDefault);
+  proxy_->GetRegistrationState(nullptr, callback, kTimeoutDefault);
 }
 
 void CellularCapabilityCDMA::OnActivateReply(