s390: 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>
diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
index 8800cf09..635d677 100644
--- a/arch/s390/boot/Makefile
+++ b/arch/s390/boot/Makefile
@@ -6,7 +6,7 @@
 			tr -c '[0-9A-Za-z]' '_'`__`date | \
 			tr -c '[0-9A-Za-z]' '_'`_t
 
-EXTRA_CFLAGS  := -DCOMPILE_VERSION=$(COMPILE_VERSION) -gstabs -I.
+ccflags-y  := -DCOMPILE_VERSION=$(COMPILE_VERSION) -gstabs -I.
 
 targets := image
 targets += bzImage