esp32/machine_timer: Fix ESP32C3 timer period doubling.

The original ESP32 only supports timer source clock APB so it doesn't need
and doesn't have a clk_src field.

The ESP32C3 supports timer source clock APB and XTAL so it does have a
clk_src field, and this needs to be configured to get the correct period.

Fixes #8084.

ports/esp32/machine_timer.c

@@ -189,6 +189,9 @@ STATIC void machine_timer_enable(machine_timer_obj_t *self) {
     config.divider = TIMER_DIVIDER;
     config.intr_type = TIMER_INTR_LEVEL;
     config.counter_en = TIMER_PAUSE;
+    #if SOC_TIMER_GROUP_SUPPORT_XTAL
+    config.clk_src = TIMER_SRC_CLK_APB;
+    #endif
 
     check_esp_err(timer_init(self->group, self->index, &config));
     check_esp_err(timer_set_counter_value(self->group, self->index, 0x00000000));