Edge AI - Modify micro speech example MIC gain on NXP FRDM-K66F for better accuracy.

 The example code recognize accuracy is lower than I expect. So I try to increase microphone gain from 0 dB to +6 dB and the result is better now.

1. Change DA7212 configuration in tensorflow/lite/micro/examples/micro_speech/nxp_k66f/audio_provider.cc

volatile uint8_t g_da7212_register_config[da7212ConfigurationSize][2] = {

...

   {0x34, 0x07},                              // Change MIXIN to 6 dB

    {0x35, 0x07},                         // Change MIXIN to 6 dB

....

2. Build and flash new binary to NXP_K66F board and test.

Ref 

DA7212 datasheet