#234: Update deck SPI log speed to bellow 2MHz

Required for flow deck and does not affect other decks (the low
speed is used only at startup by the Loco positioning deck)

src/deck/api/deck_spi.c

@@ -198,7 +198,7 @@ void spiConfigureSlow()
   SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
   SPI_InitStructure.SPI_CRCPolynomial = 0; // Not used
 
-  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_32; //~2.7 MHz
+  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64; //~1.35 MHz
   SPI_Init(SPI, &SPI_InitStructure);
 }