tools/nolibc: fix error return value of clock_nanosleep()

tools/nolibc: fix error return value of clock_nanosleep()

clock_nanosleep() returns a positive error value. Unlike other libc
functions it *does not* return -1 nor set errno.

Fix the return value and also adapt nanosleep().

Fixes: 7c02bc4088af ("tools/nolibc: add support for clock_nanosleep() and nanosleep()")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250731-nolibc-clock_nanosleep-ret-v1-1-9e4af7855e61@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>