[MIPS] mtx-1: Enable -Werror.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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