Clear UART read buffer before sending next command (#6200)

esphome/components/fingerprint_grow/fingerprint_grow.cpp

@@ -336,6 +336,8 @@ void FingerprintGrowComponent::aura_led_control(uint8_t state, uint8_t speed, ui
 }
 
 uint8_t FingerprintGrowComponent::send_command_() {
+  while (this->available())
+    this->read();
   this->write((uint8_t) (START_CODE >> 8));
   this->write((uint8_t) (START_CODE & 0xFF));
   this->write(this->address_[0]);