PWM timing off by 1

[snakehand]

I was trying to generate a 512kHz PWM signal from a 64MHz AHB clock, but when verifying the signal in the laboratory,
I found that the frequency was off, in a way consistent with the the ARR being off by one.

stm32l4xx-hal/src/pwm.rs

Line 202 in bf2ded1

// maybe this is all u32? also, why no `- 1` vs `timer.rs`?

This situation is also alluded to in the linked comment.

Changing line 200 to :

let ticks = clk / freq - 1;

Gave me the correct output frequency. I intend to make a PR linked to this issue.