selftests/nolibc: use INT_MAX instead of __INT_MAX__

nolibc now has INT_MAX in stdint.h, so, don't mix INT_MAX and
__INT_MAX__, unify them to INT_MAX.

Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>