fix Feather M4 I2S pins (arduino#80)

Author: caternuson

Diff for: variants/feather_m4/variant.h

@@ -175,10 +175,11 @@ static const uint8_t SCL = PIN_WIRE_SCL;
 #define I2S_DEVICE          0
 #define I2S_CLOCK_GENERATOR 3
 
-#define PIN_I2S_SDO          (5u)
-#define PIN_I2S_SDI          PIN_SPI_MOSI
-#define PIN_I2S_SCK          PIN_A2
-#define PIN_I2S_FS           PIN_SPI_MISO
+#define PIN_I2S_SDO          (11u)
+#define PIN_I2S_SDI          (12u)
+#define PIN_I2S_SCK          PIN_SERIAL1_TX
+#define PIN_I2S_FS           (10u)
+#define PIN_I2S_MCK          PIN_SERIAL1_RX
 
 //QSPI Pins
 #define PIN_QSPI_SCK    (34u)