PM: Use proper ccflag flag in kernel/power/Makefile

Use the ccflags-$ flag instead of EXTRA_CFLAGS because EXTRA_CFLAGS is
deprecated and should now be switched.  According to
(documentation/kbuild/makefiles.txt).

Signed-off-by: Tracey Dent <tdent48227@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

kernel/power/Makefile

@@ -1,7 +1,4 @@
-
-ifeq ($(CONFIG_PM_DEBUG),y)
-EXTRA_CFLAGS	+=	-DDEBUG
-endif
+ccflags-$(CONFIG_PM_DEBUG)	:=	-DDEBUG
 
 obj-$(CONFIG_PM)		+= main.o
 obj-$(CONFIG_PM_SLEEP)		+= console.o