imagebuilder: fix sstrip

Without an absolute path to staging_dir/host/bin/sstrip the Makefile
tries to run a host installed version of sstrip, which is likely not
available.

Signed-off-by: Paul Spooren <[email protected]>

target/imagebuilder/Makefile

@@ -90,7 +90,7 @@ endif
 	(cd $(PKG_BUILD_DIR); find staging_dir/host/bin/ $(IB_LDIR)/scripts/dtc/ -type f | \
 		$(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(PKG_BUILD_DIR)/staging_dir/host)
 	$(CP) $(TOPDIR)/staging_dir/host/lib/libfakeroot* $(PKG_BUILD_DIR)/staging_dir/host/lib
-	STRIP=sstrip $(SCRIPT_DIR)/rstrip.sh $(PKG_BUILD_DIR)/staging_dir/host/bin/
+	STRIP=$(STAGING_DIR_HOST)/bin/sstrip $(SCRIPT_DIR)/rstrip.sh $(PKG_BUILD_DIR)/staging_dir/host/bin/
 	(cd $(BUILD_DIR); \
 		tar -I '$(STAGING_DIR_HOST)/bin/xz -7e -T$(if $(filter 1,$(NPROC)),2,0)' -cf $@ $(IB_NAME) \
 		--mtime="$(shell date --date=@$(SOURCE_DATE_EPOCH))"; \