workqueue: avoid unguarded 64-bit division

The printk() requires a division that is not allowed on 32-bit architectures:

x86_64-linux-ld: lib/test_workqueue.o: in function `test_workqueue_init':
test_workqueue.c:(.init.text+0x36f): undefined reference to `__udivdi3'

Use div_u64() to print the resulting elapsed microseconds.

Fixes: 24b2e73 ("workqueue: add test_workqueue benchmark module")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
(cherry picked from commit c6890f3)
Signed-off-by: Carol L Soto <csoto@nvidia.com>

Author: arndb

lib/test_workqueue.c

@@ -242,7 +242,7 @@ static int __init run_bench(int n_threads, const char *scope, const char *label)
 
 	pr_info("test_workqueue:   %-16s %llu items/sec\tp50=%llu\tp90=%llu\tp95=%llu ns\n",
 		label,
-		elapsed_us ? total_items * 1000000ULL / elapsed_us : 0,
+		elapsed_us ? div_u64(total_items * 1000000ULL, elapsed_us) : 0,
 		all_latencies[total_items * 50 / 100],
 		all_latencies[total_items * 90 / 100],
 		all_latencies[total_items * 95 / 100]);