Increase charge pump frequency to 500 Hz

This change reduces the voltage drop with higher loads, for example if
both the solar and the load switch are on at the same time.

src/charge_pump.c

@@ -32,7 +32,7 @@ void charge_pump_init(void)
 	timer_set_prescaler(TIM1, 48 - 1); // Timer runs at 1 MHz
 
 	// auto-reload value
-	timer_set_period(TIM1, 10000 - 1); // overflow every 10000 cycles = 100 Hz
+	timer_set_period(TIM1, 2000 - 1); // overflow every 2000 cycles = 500 Hz
 
 	// output compare value
 	timer_set_oc_value(TIM1, TIM_OC1, 100); // High for 100 cycles = 100 μs