[flutter] Fix GN typo

Typo from https://dart-review.googlesource.com/c/sdk/+/164320 was not
caught on the Dart CQ.

dart_native_api.c (does not exist) should have been dart_api_dl.c.

Fix verified with Flutter build locally.

Change-Id: I7e37e4da27c02a2800ff36fd67e1be1575714c9c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164560
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Clement Skau <cskau@google.com>
diff --git a/runtime/BUILD.gn b/runtime/BUILD.gn
index 1df37c6..5c2a3a9 100644
--- a/runtime/BUILD.gn
+++ b/runtime/BUILD.gn
@@ -207,8 +207,8 @@
   public_configs = [ ":dart_public_config" ]
   sources = [
     "include/dart_api.h",
+    "include/dart_api_dl.c",
     "include/dart_api_dl.h",
-    "include/dart_native_api.c",
     "include/dart_native_api.h",
     "include/dart_tools_api.h",
     "include/dart_version.h",