tools: Include U-Boot libfdt headers from their actual path

There are no headers for libfdt in lib/libfdt, as they are instead
located in scripts/dtc/libfdt. Specifying lib/libfdt for headers
inclusion in host tools results in using the system libfdt headers,
which is not what we want. Change this to the proper path.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
diff --git a/tools/Makefile b/tools/Makefile
index d3387fa..f38f68e 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -244,7 +244,7 @@
 #
 HOST_EXTRACFLAGS += -include $(srctree)/include/compiler.h \
 		$(patsubst -I%,-idirafter%, $(filter -I%, $(UBOOTINCLUDE))) \
-		-I$(srctree)/lib/libfdt \
+		-I$(srctree)/scripts/dtc/libfdt \
 		-I$(srctree)/tools \
 		-DUSE_HOSTCC \
 		-D__KERNEL_STRICT_NAMES \