mm: add casts to/from gfp_t in gfp_to_alloc_flags()

This removes following warning from sparse:

 mm/page_alloc.c:1934:9: warning: restricted gfp_t degrades to integer
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -1932,7 +1932,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	const gfp_t wait = gfp_mask & __GFP_WAIT;
 
 	/* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
-	BUILD_BUG_ON(__GFP_HIGH != ALLOC_HIGH);
+	BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
 
 	/*
 	 * The caller may dip into page reserves a bit more if the caller
@@ -1940,7 +1940,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	 * policy or is asking for __GFP_HIGH memory.  GFP_ATOMIC requests will
 	 * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
 	 */
-	alloc_flags |= (gfp_mask & __GFP_HIGH);
+	alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
 
 	if (!wait) {
 		alloc_flags |= ALLOC_HARDER;