swift: Point to swift's kernel device tree

The kernel device tree for swift has been merged upstream.

Tested:
    Output of "bitbake obmc-phosphor-image -e":
    # pre-expansion value:
    #   "${KMACHINE}-bmc-opp-${MACHINE}.dtb"
    KERNEL_DEVICETREE="aspeed-bmc-opp-swift.dtb"

Change-Id: Ie56a243e8635fdb616ed930f0389f77e61271abf
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meta-witherspoon/conf/machine/swift.conf b/meta-witherspoon/conf/machine/swift.conf
index 4a84b0c..6b5b7ce 100644
--- a/meta-witherspoon/conf/machine/swift.conf
+++ b/meta-witherspoon/conf/machine/swift.conf
@@ -1,9 +1,7 @@
 require conf/machine/witherspoon.conf
 
-# TODO Change to ${KMACHINE}-bmc-opp-swift.dtb when the device tree is available
-KERNEL_DEVICETREE = "${KMACHINE}-bmc-opp-witherspoon.dtb"
+KERNEL_DEVICETREE = "${KMACHINE}-bmc-opp-${MACHINE}.dtb"
 
-# TODO Update once a Swift MRW is available
 PHOSPHOR_MRW_LICENSE = "Apache-2.0"
 PHOSPHOR_MRW_LIC_FILES_CHKSUM = "file://LICENSE;md5=e3fc50a88d0a364313df4b21ef20c29e"
 PHOSPHOR_MRW_URI = "git://git@github.com/open-power/swift-xml;protocol=ssh"