Integer saturation in Timer::start

[apatrushev]

The following code snippets should be equivalent in result, but they are not:

let mut timer = Timer::new(cx.device.TIM2, clocks, &mut rcc.apb1);
timer.enable_interrupt(Event::Update);
timer.start(1.milliseconds());

let mut timer = Timer::new(cx.device.TIM2, clocks, &mut rcc.apb1);
timer.enable_interrupt(Event::Update);
timer.start(1000.microseconds());

This happens due to the integer saturation in following line:

stm32f3xx-hal/src/timer.rs

Line 280 in 8933e11

let ticks = clock.integer().saturating_mul(timeout.integer()) * *timeout.scaling_factor();

Yes, the simplest answer would be "don't do that!", but this also happens with legitimate examples like 100.microseconds().

Perhaps one of the following fixes can be applied:

• ticks can be extended to u64 (more precise result)
• change the multiplication order as follows (better performance and code size?)

let ticks = ((clock.integer() * *timeout.scaling_factor()) as u32).saturating_mul(timeout.integer());