Be more careful when configuring MCLK

output_i2s.cpp

@@ -298,6 +298,7 @@ void AudioOutputI2S::config_i2s(void)
 
 	// enable MCLK output
 	I2S0_MCR = I2S_MCR_MICS(MCLK_SRC) | I2S_MCR_MOE;
+	while (I2S0_MCR & I2S_MCR_DUF) ;
 	I2S0_MDR = I2S_MDR_FRACT((MCLK_MULT-1)) | I2S_MDR_DIVIDE((MCLK_DIV-1));
 
 	// configure transmitter

output_i2s_quad.cpp

@@ -293,6 +293,7 @@ void AudioOutputI2SQuad::config_i2s(void)
 
 	// enable MCLK output
 	I2S0_MCR = I2S_MCR_MICS(MCLK_SRC) | I2S_MCR_MOE;
+	while (I2S0_MCR & I2S_MCR_DUF) ;
 	I2S0_MDR = I2S_MDR_FRACT((MCLK_MULT-1)) | I2S_MDR_DIVIDE((MCLK_DIV-1));
 
 	// configure transmitter

output_spdif.cpp

@@ -343,6 +343,7 @@ void AudioOutputSPDIF::config_SPDIF(void)
 
 	// enable MCLK output
 	I2S0_MCR = I2S_MCR_MICS(MCLK_SRC) | I2S_MCR_MOE;
+	while (I2S0_MCR & I2S_MCR_DUF) ;
 	I2S0_MDR = I2S_MDR_FRACT((MCLK_MULT-1)) | I2S_MDR_DIVIDE((MCLK_DIV-1));
 
 	// configure transmitter