meta-ibm: sbp1: make required kernel dts change

This system still just utilizes the evb dts but it does need to be
updated for the latest 6.5 changes that moved these to an aspeed
sub-directory.

Tested:
- Confirmed sbp1 builds again

Change-Id: Ide9dde8233255f3dc06348a586d15b943025f834
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/meta-ibm/meta-sbp1/conf/machine/sbp1.conf b/meta-ibm/meta-sbp1/conf/machine/sbp1.conf
index c3d2de5..4742db7 100644
--- a/meta-ibm/meta-sbp1/conf/machine/sbp1.conf
+++ b/meta-ibm/meta-sbp1/conf/machine/sbp1.conf
@@ -1,5 +1,5 @@
 KMACHINE = "aspeed"
-KERNEL_DEVICETREE = "${KMACHINE}-ast2600-evb.dtb"
+KERNEL_DEVICETREE = "aspeed/${KMACHINE}-ast2600-evb.dtb"
 
 UBOOT_MACHINE = "ast2600_openbmc_spl_defconfig"
 UBOOT_DEVICETREE = "ast2600a1-evb"