mm: fix up sparse warning in gfpflags_allow_blocking

sparse says:

    include/linux/gfp.h:274:26: warning: incorrect type in return expression (different base types)
    include/linux/gfp.h:274:26:    expected bool
    include/linux/gfp.h:274:26:    got restricted gfp_t

...add a forced cast to silence the warning.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/gfp.h

@@ -271,7 +271,7 @@ static inline int gfpflags_to_migratetype(const gfp_t gfp_flags)
 
 static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
 {
-	return gfp_flags & __GFP_DIRECT_RECLAIM;
+	return (bool __force)(gfp_flags & __GFP_DIRECT_RECLAIM);
 }
 
 #ifdef CONFIG_HIGHMEM