[MIPS] IP22: Enable -Werror.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/sgi-ip22/Makefile

@@ -7,3 +7,5 @@ obj-y	+= ip22-mc.o ip22-hpc.o ip22-int.o ip22-berr.o \
 	   ip22-time.o ip22-nvram.o ip22-platform.o ip22-reset.o ip22-setup.o
 
 obj-$(CONFIG_EISA)	+= ip22-eisa.o
+
+EXTRA_CFLAGS += -Werror