Fix clang 7.0 warnings.

* Cast EXPECT_EQ arguments to the same signed/unsigned type.

Test: Build
Change-Id: I1055215045fb0904438d0a71bde034fab99111cc
diff --git a/libs/vr/libpdx/service_tests.cpp b/libs/vr/libpdx/service_tests.cpp
index c7412b7..e623abf 100644
--- a/libs/vr/libpdx/service_tests.cpp
+++ b/libs/vr/libpdx/service_tests.cpp
@@ -180,8 +180,8 @@
   EXPECT_EQ(kTestTid, message.GetThreadId());
   EXPECT_EQ(kTestCid, message.GetChannelId());
   EXPECT_EQ(kTestMid, message.GetMessageId());
-  EXPECT_EQ(kTestEuid, message.GetEffectiveUserId());
-  EXPECT_EQ(kTestEgid, message.GetEffectiveGroupId());
+  EXPECT_EQ((unsigned) kTestEuid, message.GetEffectiveUserId());
+  EXPECT_EQ((unsigned) kTestEgid, message.GetEffectiveGroupId());
   EXPECT_EQ(kTestOp, message.GetOp());
   EXPECT_EQ(service_, message.GetService());
   EXPECT_EQ(test_channel, message.GetChannel());