posix: clock: fix 32-bit time_t overflow in __z_clock_nanosleep

Nanosecond time calculation overflows if the libc has 32-bit time_t.
One such libc is the classic ARC MWDT one, but there might be others.

Signed-off-by: Ilya Tagunov <[email protected]>

Author: tagunil

lib/posix/options/clock.c

@@ -222,7 +222,7 @@ static int __z_clock_nanosleep(clockid_t clock_id, int flags, const struct times
 		ns = rqtp->tv_nsec + NSEC_PER_SEC
 			+ k_sleep(K_SECONDS(rqtp->tv_sec - 1)) * NSEC_PER_MSEC;
 	} else {
-		ns = rqtp->tv_sec * NSEC_PER_SEC + rqtp->tv_nsec;
+		ns = (uint64_t)rqtp->tv_sec * NSEC_PER_SEC + rqtp->tv_nsec;
 	}
 
 	uptime_ns = k_ticks_to_ns_ceil64(sys_clock_tick_get());