project: mdm9640: Turn on Werror

Ensure that code compiles warnings free for mdm9640.

Change-Id: I61fe3eb2dc754c04582c494abece1c69f2334b8c
diff --git a/project/mdm9640.mk b/project/mdm9640.mk
index c8381c3..24addd8 100644
--- a/project/mdm9640.mk
+++ b/project/mdm9640.mk
@@ -44,3 +44,6 @@
 ifeq ($(ENABLE_SMD_SUPPORT),1)
 DEFINES += SMD_SUPPORT=1
 endif
+
+# Turn on Werror
+CFLAGS += -Werror