Use -Werror in hardware/libhardware

* Remove unused local variables and function.
* Fix unused return value warning.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I269eca76cda2222c7a0176e85e92df0bb0924a0e
diff --git a/modules/tv_input/Android.bp b/modules/tv_input/Android.bp
index 4d2369e..b9d8afa 100644
--- a/modules/tv_input/Android.bp
+++ b/modules/tv_input/Android.bp
@@ -22,4 +22,5 @@
         "liblog",
     ],
     srcs: ["tv_input.cpp"],
+    cflags: ["-Wall", "-Werror"],
 }