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

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sibyte/common/Makefile b/arch/mips/sibyte/common/Makefile
index 8a06a4f..f8ae300 100644
--- a/arch/mips/sibyte/common/Makefile
+++ b/arch/mips/sibyte/common/Makefile
@@ -3,3 +3,4 @@
 obj-$(CONFIG_SIBYTE_TBPROF)		+= sb_tbprof.o
 
 EXTRA_AFLAGS := $(CFLAGS)
+EXTRA_CFLAGS += -Werror