Use -Werror in hardware/libhardware/modules

* Remove unused local variables.
* Remove or comment out unused static functions.
* Fix trivial bugs found by unused value warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I99389b883c89551850180d25241a35a40bb77b26
diff --git a/modules/input/evdev/Android.mk b/modules/input/evdev/Android.mk
index cb12964..df16b53 100644
--- a/modules/input/evdev/Android.mk
+++ b/modules/input/evdev/Android.mk
@@ -55,7 +55,7 @@
     liblog
 
 LOCAL_CLANG := true
-LOCAL_CPPFLAGS += -Wno-unused-parameter
+LOCAL_CPPFLAGS += -Wall -Werror -Wno-unused-parameter
 
 LOCAL_MODULE_TAGS := optional