need using ccflags-y instead of EXTRA_CFLAGS
can reference scripts/checkpatch.pl (1755..1766)
when make EXTRA_CFLAGS=-W, the compiling issue will be occured.
Signed-off-by: Chen Gang <gang.chen@asianux.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>