kcsan: Fix printk format string

Printing a 'long' variable using the '%d' format string is wrong
and causes a warning from gcc:

kernel/kcsan/kcsan_test.c: In function 'nthreads_gen_params':
include/linux/kern_levels.h:5:25: error: format '%d' expects argument of type 'int', but argument 3 has type 'long int' [-Werror=format=]

Use the appropriate format modifier.

Fixes: f6a14914

 ("kcsan: Switch to KUNIT_CASE_PARAM for parameterized tests")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20210421135059.3371701-1-arnd@kernel.org