[Fuchsia] Fix wrong variable fuchsia_additional_boot_images

Include the path provided by each image rather than the whole list itself.

Change-Id: Ib13bc70af0a542a7d23a71d8dd1db0ffb006077c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462677Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Auto-Submit: Chong Gu <chonggu@google.com>
Cr-Commit-Position: refs/heads/master@{#815786}

build/config/fuchsia/generate_runner_scripts.gni

@@ -129,7 +129,7 @@ template("fuchsia_package_runner") {
     }
 
     foreach(fuchsia_additional_boot_image, fuchsia_additional_boot_images) {
-      data += [ "${fuchsia_additional_boot_images}/" ]
+      data += [ "${fuchsia_additional_boot_image}/" ]
     }
 
     executable_args = []