[flatbuffer] fix deps type in flatbuffer.gni

Header generating action needs to be in public_deps

Bug: 931596
Change-Id: Ie69a72a1ab22d839f337e9a3cb7cf105fec43163
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1508472
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638557}

third_party/flatbuffers/flatbuffer.gni

@@ -128,10 +128,8 @@ template("flatbuffer") {
     public_deps = [
       # The generated headers reference headers within FlatBuffers, so
       # dependencies must be able to find those headers too.
-      "//third_party/flatbuffers",
-    ]
-    deps = [
       ":$action_name",
+      "//third_party/flatbuffers",
     ]
 
     # This will link any libraries in the deps (the use of invoker.deps in the