[pwm, rtl] PWM RTL fix for duty cycle overflow/underflow
[pwm, rtl] PWM RTL fix for duty cycle overflow/underflow

  - Fix the PWM RTL duty cycle overflow/underflow issue to match the spec
  - Fixes #13434

Signed-off-by: Muqing Liu <b1c0f8d5c8fd5df55dfdf439926eb15b5e395e02@wdc.com>

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