Replace IInterface::asBinder() with a static

so we can do NULL checks again, and update calls to IInterface::asBinder()
to use the new static version.

Change-Id: Ia7b10eb38ca55b72278bfd33d3bf647f338b4e6a
diff --git a/libs/binder/IServiceManager.cpp b/libs/binder/IServiceManager.cpp
index 7b1b0e7..3c716df 100644
--- a/libs/binder/IServiceManager.cpp
+++ b/libs/binder/IServiceManager.cpp
@@ -87,7 +87,7 @@
             }
             
             // Is this a permission failure, or did the controller go away?
-            if (pc->asBinder()->isBinderAlive()) {
+            if (IInterface::asBinder(pc)->isBinderAlive()) {
                 ALOGW("Permission failure: %s from uid=%d pid=%d",
                         String8(permission).string(), uid, pid);
                 return false;