implement retriving duty.

Description: When disabling the pwm and enabling again, it is required to restart the sequence. If the previous duty is not known, it is not possible to turn on the pwm again

embassy-nrf/src/pwm.rs

@@ -736,6 +736,11 @@ impl<'d, T: Instance> SimplePwm<'d, T> {
         r.enable.write(|w| w.enable().disabled());
     }
 
+    /// Returns the current duty of the channel
+    pub fn duty(&self, channel: usize) -> u16 {
+        self.duty[channel]
+    }
+
     /// Sets duty cycle (15 bit) for a PWM channel.
     pub fn set_duty(&mut self, channel: usize, duty: u16) {
         let r = T::regs();