display: Fix warnings, make warnings as errors

Change-Id: I61f22765b04112be48e62135db930c415c9c7d37
diff --git a/common.mk b/common.mk
index e5cc394..99dfbdf 100644
--- a/common.mk
+++ b/common.mk
@@ -15,6 +15,8 @@
 
 #Common C flags
 common_flags := -DDEBUG_CALC_FPS -Wno-missing-field-initializers
+common_flags += -Werror
+
 ifeq ($(ARCH_ARM_HAVE_NEON),true)
     common_flags += -D__ARM_HAVE_NEON
 endif