uboot: fix build for older uboot source trees

The change in commit bf73334 only works
for newer uboot source trees. Add a check that scripts/dtc/libfdt
directory exists before making this change.

[Peter: add comment explaining why]
Signed-off-by: Stefan Becker <[email protected]>
Signed-off-by: Peter Korsgaard <[email protected]>

(cherry picked from commit f437bf5)
Signed-off-by: Peter Korsgaard <[email protected]>

Author: stefanb2

boot/uboot/uboot.mk

@@ -191,8 +191,12 @@ UBOOT_POST_PATCH_HOOKS += UBOOT_APPLY_LOCAL_PATCHES
 # This is equivalent to upstream commit
 # http://git.denx.de/?p=u-boot.git;a=commitdiff;h=e0d20dc1521e74b82dbd69be53a048847798a90a. It
 # fixes a build failure when libfdt-devel is installed system-wide.
+# This only works when scripts/dtc/libfdt exists (E.G. versions containing
+# http://git.denx.de/?p=u-boot.git;a=commitdiff;h=c0e032e0090d6541549b19cc47e06ccd1f302893)
 define UBOOT_FIXUP_LIBFDT_INCLUDE
-	$(SED) 's%-I$$(srctree)/lib/libfdt%-I$$(srctree)/scripts/dtc/libfdt%' $(@D)/tools/Makefile
+	if [ -d $(@D)/scripts/dtc/libfdt ]; then \
+		$(SED) 's%-I$$(srctree)/lib/libfdt%-I$$(srctree)/scripts/dtc/libfdt%' $(@D)/tools/Makefile; \
+	fi
 endef
 UBOOT_POST_PATCH_HOOKS += UBOOT_FIXUP_LIBFDT_INCLUDE