fix(xclk): Zero init ledc_channel_config_t for forward compatibility

LEDC driver was extended in espressif/esp-idf@4a90deb with new config structure members.
We must zero init the config struct to get default behavior.

target/xclk.c

@@ -47,7 +47,7 @@ esp_err_t camera_enable_out_clock(const camera_config_t* config)
     }
 
     g_ledc_channel = config->ledc_channel;
-    ledc_channel_config_t ch_conf;
+    ledc_channel_config_t ch_conf = {0};
     ch_conf.gpio_num = config->pin_xclk;
     ch_conf.speed_mode = LEDC_LOW_SPEED_MODE;
     ch_conf.channel = config->ledc_channel;