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

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mips-boards/sead/Makefile b/arch/mips/mips-boards/sead/Makefile
index 224bb84..3682fe2 100644
--- a/arch/mips/mips-boards/sead/Makefile
+++ b/arch/mips/mips-boards/sead/Makefile
@@ -24,3 +24,5 @@
 #
 
 obj-y		:= sead_int.o sead_setup.o
+
+EXTRA_CFLAGS += -Werror