scripts: fix gfp-translate for recent changes to gfp.h

The recent changes to gfp.h to satisfy sparse broke scripts/gfp-translate.
This patch fixes it up to work with old and new versions of gfp.h .

[akpm@linux-foundation.org: use `grep -q', per WANG Cong]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: Namhyung Kim <namhyung@gmail.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>