mips: change to new flag variable

Replace EXTRA_CFLAGS with ccflags-y.

Signed-off-by: matt mooney <mfm@muteddisk.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

arch/mips/fw/arc/Makefile

@@ -9,4 +9,4 @@ lib-$(CONFIG_ARC_MEMORY)	+= memory.o
 lib-$(CONFIG_ARC_CONSOLE)	+= arc_con.o
 lib-$(CONFIG_ARC_PROMLIB)	+= promlib.o
 
-EXTRA_CFLAGS			+= -Werror
+ccflags-y			:= -Werror