fw/spi.c (spi_init): revert the SPI speed increase (caused instability)

Some more testing showed that transfers would get stuck after ~40 packets.
Need to find out what happened before trying this again.

fw/spi.c

@@ -26,11 +26,11 @@
 
 void spi_init(void)
 {
-	/* SPI mode 0, MSB first, fosc/2 */
+	/* SPI mode 0, MSB first, fosc/4 */
 	SPCR =
 	    1 << SPE |	/* enable SPI */
 	    1 << MSTR;	/* master */
-	SPSR = 1 << SPI2X; /* enable for fosc/2 */
+//	SPSR = 1 << SPI2X; /* enable for fosc/2 */
 }