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

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip32/Makefile b/arch/mips/sgi-ip32/Makefile
index 60f0227..31c9aa1 100644
--- a/arch/mips/sgi-ip32/Makefile
+++ b/arch/mips/sgi-ip32/Makefile
@@ -5,3 +5,5 @@
 
 obj-y	+= ip32-berr.o ip32-irq.o ip32-platform.o ip32-setup.o ip32-reset.o \
 	   crime.o ip32-memory.o
+
+EXTRA_CFLAGS += -Werror