kcsan: use u64 instead of cycles_t

cycles_t has a different type across architectures: unsigned int,
unsinged long, or unsigned long long. Depending on architecture this
will generate this warning:

kernel/kcsan/debugfs.c: In function ‘microbenchmark’:
./include/linux/kern_levels.h:5:25: warning: format ‘%llu’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘cycles_t’ {aka ‘long unsigned int’} [-Wformat=]

To avoid this simply change the type of cycle to u64 in microbenchmark(),
since u64 is of type unsigned long long for all architectures.
Acked-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20210729142811.1309391-1-hca@linux.ibm.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

kernel/kcsan/debugfs.c

@@ -64,7 +64,7 @@ static noinline void microbenchmark(unsigned long iters)
 {
 	const struct kcsan_ctx ctx_save = current->kcsan_ctx;
 	const bool was_enabled = READ_ONCE(kcsan_enabled);
-	cycles_t cycles;
+	u64 cycles;
 
 	/* We may have been called from an atomic region; reset context. */
 	memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));