I2S for LPC1768 with typo patch for I2S rx clock pin setup in I2S.cpp line 492 - used for microphone demo

Dependents:   i2s_microphone LPC1768_MicrophoneSensing Receiver

Fork of I2S by Giles Barton-Owen

Fixes I2S rx clock typo in original I2S library code - see line 494 The two I2S RX clock pin options were swapped in the pin setup code. See https://os.mbed.com/users/4180_1/notebook/using-an-i2s-microphone---sph0645lm4h/