[MIPS] Use -Werror on subdirectories which build cleanly.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/au1000/common/Makefile b/arch/mips/au1000/common/Makefile
index 4c35525..90e2d7a 100644
--- a/arch/mips/au1000/common/Makefile
+++ b/arch/mips/au1000/common/Makefile
@@ -12,3 +12,5 @@
 
 obj-$(CONFIG_KGDB)		+= dbg_io.o
 obj-$(CONFIG_PCI)		+= pci.o
+
+EXTRA_CFLAGS += -Werror