[MIPS] Pb1200: Enable -Werror.

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

arch/mips/au1000/pb1200/Makefile

@@ -3,3 +3,5 @@
 #
 
 lib-y := init.o board_setup.o irqmap.o
+
+EXTRA_CFLAGS += -Werror