Fix the last warnings in frameworks/av/ drm code.

- index is always positive so no need to check > 0
- args parameters are unused.

Bug: 27151704
Change-Id: Ia4c23e1fc4eaef47f38526574b35ccfea9c92177
diff --git a/drm/drmserver/Android.mk b/drm/drmserver/Android.mk
index 9b15f93..3b8bb04 100644
--- a/drm/drmserver/Android.mk
+++ b/drm/drmserver/Android.mk
@@ -36,6 +36,8 @@
     $(TOP)/frameworks/av/drm/libdrmframework/include \
     $(TOP)/frameworks/av/drm/libdrmframework/plugins/common/include
 
+LOCAL_CFLAGS += -Wall -Wextra -Werror
+
 LOCAL_MODULE:= drmserver
 
 LOCAL_MODULE_TAGS := optional