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

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip27/Makefile b/arch/mips/sgi-ip27/Makefile
index 7ce76e2..e0a6871d 100644
--- a/arch/mips/sgi-ip27/Makefile
+++ b/arch/mips/sgi-ip27/Makefile
@@ -9,3 +9,5 @@
 obj-$(CONFIG_EARLY_PRINTK)	+= ip27-console.o
 obj-$(CONFIG_KGDB)		+= ip27-dbgio.o
 obj-$(CONFIG_SMP)		+= ip27-smp.o
+
+EXTRA_CFLAGS += -Werror