Power: remove warnings from VTS test.

Test: pass
Change-Id: I1851d7f7e330ed2d9f92a35e29842cf04b13601f
diff --git a/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp b/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
index 757367b..9309a5f 100644
--- a/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
+++ b/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
@@ -83,7 +83,7 @@
 
   char governors[1024];
   unsigned len = read(fd2, governors, 1024);
-  ASSERT_LE(0, len);
+  ASSERT_LE(0u, len);
   governors[len] = '\0';
 
   char *saveptr;