[MIPS] mtx-1: Enable -Werror.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/au1000/mtx-1/Makefile b/arch/mips/au1000/mtx-1/Makefile
index afa7007d..85a9094 100644
--- a/arch/mips/au1000/mtx-1/Makefile
+++ b/arch/mips/au1000/mtx-1/Makefile
@@ -9,3 +9,5 @@
 
 lib-y := init.o board_setup.o irqmap.o
 obj-y := platform.o
+
+EXTRA_CFLAGS += -Werror