linux-raspberrypi: Drop unnecessary code

* The kerneltype variable is not used anywhere after being set.

* The manipulation of KERNEL_DEVICETREE is effectively a no-op, we read the
  current value in get_dts() and store this back into the same variable.

Signed-off-by: Paul Barker <pbarker@toganlabs.com>

classes/sdcard_image-rpi.bbclass

@@ -86,7 +86,7 @@ IMAGE_CMD_rpi-sdimg () {
 	echo "Creating filesystem with Boot partition ${BOOT_SPACE_ALIGNED} KiB and RootFS $ROOTFS_SIZE KiB"
 
 	# Check if we are building with device tree support
-	DTS="${@get_dts(d)}"
+	DTS="${KERNEL_DEVICETREE}"
 
 	# Initialize sdcard image file
 	dd if=/dev/zero of=${SDIMG} bs=1024 count=0 seek=${SDIMG_SIZE}