configs/broadcom_northstar_defconfig: adjust DTS paths

Starting with kernel release v6.5 ARM DTS files are placed in vendor
subdirectories (Linux commit 724ba6751532 ("ARM: dts: Move .dts files to
vendor sub-directories")).

This fixes:
make[3]: *** No rule to make target 'arch/arm/boot/dts/bcm4708-smartrg-sr400ac.dtb'.  Stop.
make[2]: *** [Makefile:1384: bcm4708-smartrg-sr400ac.dtb] Error 2
make[3]: *** No rule to make target 'arch/arm/boot/dts/bcm47094-luxul-xwr-3150-v1.dtb'.  Stop.
make[2]: *** [Makefile:1384: bcm47094-luxul-xwr-3150-v1.dtb] Error 2

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/broadcom_northstar_defconfig

@@ -5,7 +5,7 @@ BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/broadcom/northstar/linux.config"
 BR2_LINUX_KERNEL_APPENDED_ZIMAGE=y
-BR2_LINUX_KERNEL_INTREE_DTS_NAME="bcm4708-smartrg-sr400ac bcm47094-luxul-xwr-3150-v1"
+BR2_LINUX_KERNEL_INTREE_DTS_NAME="broadcom/bcm4708-smartrg-sr400ac broadcom/bcm47094-luxul-xwr-3150-v1"
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_ROOTFS_UBI=y
 BR2_TARGET_ROOTFS_UBI_SUBSIZE=2048