[source] build: fix generating dtb with / in DEVICE_DTS

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/b0e6284879773e9ae407aeb7f37b9ab89e8056ab

commit b0e6284879773e9ae407aeb7f37b9ab89e8056ab
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Nov 9 14:26:24 2017 +0100

    build: fix generating dtb with / in DEVICE_DTS
    
    Fixes layerscape build error
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/image.mk | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/image.mk b/include/image.mk
index 96a8892..f4d0a15 100644
--- a/include/image.mk
+++ b/include/image.mk
@@ -440,7 +440,7 @@ define Device/Build/dtb
   ifndef BUILD_DTS_$(1)
   BUILD_DTS_$(1) := 1
   $(KDIR)/image-$(1).dtb: FORCE
-	$(call Image/BuildDTB,$(strip $(2))/$(1).dts,$$@)
+	$(call Image/BuildDTB,$(strip $(2))/$(strip $(3)).dts,$$@)
 
   image_prepare: $(KDIR)/image-$(1).dtb
   endif
@@ -450,8 +450,9 @@ endif
 
 define Device/Build/kernel
   $$(eval $$(foreach dts,$$(DEVICE_DTS), \
-	$$(call Device/Build/dtb,$$(dts), \
-		$$(if $$(DEVICE_DTS_DIR),$$(DEVICE_DTS_DIR),$$(DTS_DIR)) \
+	$$(call Device/Build/dtb,$$(notdir $$(dts)), \
+		$$(if $$(DEVICE_DTS_DIR),$$(DEVICE_DTS_DIR),$$(DTS_DIR)), \
+		$$(dts) \
 	) \
   ))