zipf: use 64-bit safe hash for zipf/pareto

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/lib/zipf.h b/lib/zipf.h
index dbcaffb..f98ad81 100644
--- a/lib/zipf.h
+++ b/lib/zipf.h
@@ -11,7 +11,7 @@
 	double zetan;
 	double pareto_pow;
 	struct frand_state rand;
-	unsigned long rand_off;
+	uint64_t rand_off;
 };
 
 void zipf_init(struct zipf_state *zs, unsigned long nranges, double theta, unsigned int seed);