libbinder: don't ignore sendDecStrong error

I am not sure why this was ignored before, but I can't think of any
reason why it should be. Fail hard fail fast.

Note: this is being submitted independently in preparation for a series
of refcount changes related to performance.

Bug: 182940634
Test: binderRpcTest
Change-Id: Ifcc0bf96952a368c4ad5620b3f1d2d17feac40c5
diff --git a/libs/binder/RpcState.cpp b/libs/binder/RpcState.cpp
index dcba837..df935fe 100644
--- a/libs/binder/RpcState.cpp
+++ b/libs/binder/RpcState.cpp
@@ -166,9 +166,7 @@
         // We have timesRecd RPC refcounts, but we only need to hold on to one
         // when we keep the object. All additional dec strongs are sent
         // immediately, we wait to send the last one in BpBinder::onLastDecStrong.
-        (void)session->sendDecStrong(address);
-
-        return OK;
+        return session->sendDecStrong(address);
     }
 
     // we don't know about this binder, so the other side of the connection