hash: make 64-bit even on 32-bit

hash: make 64-bit even on 32-bit

Fixes this warning on Windows, where unsigned long is 32-bit:

hash.h: In function ‘__hash_long’:
hash.h:58:2: warning: left shift count >= width of type
  n <<= 33;
  ^

Signed-off-by: Jens Axboe <axboe@fb.com>