Move validation code to the right spot.

As MicroDev1 pointed out the problem is a divide by zero when calculating the duty cycle.
Maybe need to check again in `common_hal_pwmio_pwmout_set_frequency()`.

Author: rsbohn

ports/esp32s2/common-hal/pwmio/PWMOut.c

@@ -63,6 +63,12 @@ pwmout_result_t common_hal_pwmio_pwmout_construct(pwmio_pwmout_obj_t *self,
     uint16_t duty,
     uint32_t frequency,
     bool variable_frequency) {
+
+    // check the frequency (avoid divide by zero below)
+    if (frequency == 0) {
+        return PWMOUT_INVALID_FREQUENCY;
+    }
+
     // Calculate duty cycle
     uint32_t duty_bits = 0;
     uint32_t interval = LEDC_APB_CLK_HZ / frequency;
@@ -129,12 +135,6 @@ pwmout_result_t common_hal_pwmio_pwmout_construct(pwmio_pwmout_obj_t *self,
         return PWMOUT_INITIALIZATION_ERROR;
     }
 
-    // check the frequency -- 0 is not valid
-    // maybe also want to reject frequency > system_clock / 2 ??
-    if (frequency == 0) {
-        return PWMOUT_INVALID_FREQUENCY;
-    }
-
     // Make reservations
     reserved_timer_freq[timer_index] = frequency;
     reserved_channels[channel_index] = timer_index;