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

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/qemu/Makefile b/arch/mips/qemu/Makefile
index 078cd30..cec24c1 100644
--- a/arch/mips/qemu/Makefile
+++ b/arch/mips/qemu/Makefile
@@ -5,3 +5,5 @@
 obj-y		= q-firmware.o q-irq.o q-mem.o q-setup.o q-reset.o
 
 obj-$(CONFIG_SMP) += q-smp.o
+
+EXTRA_CFLAGS += -Werror