Disable unused parameter warning for libinput

Also, avoid comparing values of mixed signedness.

Change-Id: I9804f69c29fcb1d0a9fe4b833ef1a569738c99fd
diff --git a/services/input/Android.mk b/services/input/Android.mk
index 6e944ef..eb2bebe 100644
--- a/services/input/Android.mk
+++ b/services/input/Android.mk
@@ -42,6 +42,8 @@
 LOCAL_C_INCLUDES := \
     external/skia/include/core
 
+LOCAL_CFLAGS += -Wno-unused-parameter
+
 LOCAL_MODULE:= libinputservice
 
 LOCAL_MODULE_TAGS := optional