make the I2C and SPI device signons distinct

apps/drivers/device/i2c.cpp

@@ -99,7 +99,7 @@ I2C::init()
 	}
 
 	// tell the world where we are
-	log("on bus %d at 0x%02x", _bus, _address);
+	log("on I2C bus %d at 0x%02x", _bus, _address);
 
 out:
 	return ret;

apps/drivers/device/spi.cpp

@@ -111,7 +111,7 @@ SPI::init()
 	}
 
 	// tell the workd where we are
-	log("on bus %d at %d", _bus, _device);
+	log("on SPI bus %d at %d", _bus, _device);
 
 out:
 	return ret;