media: cec: use us_to_ktime() where appropriate

[Why]
There are several ns_to_ktime() calls that require using nanoseconds. It is
better to replace them with us_to_ktime() to make code clear, getting rid
of multiplication by 1000.

Also the timer function code may have an integer wrap-around issue. Since
both tx_custom_low_usecs and tx_custom_high_usecs can be set to up to
9999999 from the user space via cec_pin_error_inj_parse_line(), this may
cause usecs to be overflowed when adap->monitor_pin_cnt is zero and usecs
is multiplied by 1000.

[How]
Take advantage of using an appropriate helper func us_to_ktime() instead of
ns_to_ktime() to improve readability and to make the code clearer. And this
also mitigates possible integer wrap-arounds when usecs value is too large
and it is multiplied by 1000.

Found by Linux Verification Center (linuxtesting.org) with Svace.

Signed-off-by: Vitaliy Shevtsov <v.shevtsov@mt-integration.ru>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

Author: Vitaliy Shevtsov

drivers/media/cec/core/cec-pin.c

@@ -873,19 +873,19 @@ static enum hrtimer_restart cec_pin_timer(struct hrtimer *timer)
 		if (pin->wait_usecs > 150) {
 			pin->wait_usecs -= 100;
 			pin->timer_ts = ktime_add_us(ts, 100);
-			hrtimer_forward_now(timer, ns_to_ktime(100000));
+			hrtimer_forward_now(timer, us_to_ktime(100));
 			return HRTIMER_RESTART;
 		}
 		if (pin->wait_usecs > 100) {
 			pin->wait_usecs /= 2;
 			pin->timer_ts = ktime_add_us(ts, pin->wait_usecs);
 			hrtimer_forward_now(timer,
-					ns_to_ktime(pin->wait_usecs * 1000));
+					us_to_ktime(pin->wait_usecs));
 			return HRTIMER_RESTART;
 		}
 		pin->timer_ts = ktime_add_us(ts, pin->wait_usecs);
 		hrtimer_forward_now(timer,
-				    ns_to_ktime(pin->wait_usecs * 1000));
+				    us_to_ktime(pin->wait_usecs));
 		pin->wait_usecs = 0;
 		return HRTIMER_RESTART;
 	}
@@ -1020,13 +1020,12 @@ static enum hrtimer_restart cec_pin_timer(struct hrtimer *timer)
 	if (!adap->monitor_pin_cnt || usecs <= 150) {
 		pin->wait_usecs = 0;
 		pin->timer_ts = ktime_add_us(ts, usecs);
-		hrtimer_forward_now(timer,
-				ns_to_ktime(usecs * 1000));
+		hrtimer_forward_now(timer, us_to_ktime(usecs));
 		return HRTIMER_RESTART;
 	}
 	pin->wait_usecs = usecs - 100;
 	pin->timer_ts = ktime_add_us(ts, 100);
-	hrtimer_forward_now(timer, ns_to_ktime(100000));
+	hrtimer_forward_now(timer, us_to_ktime(100));
 	return HRTIMER_RESTART;
 }