Fix incorrect indentation in version generator script.

Bug: dawn:549
Change-Id: I6eaa61c8339114fc3692251f263dea65816b618e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94528
Commit-Queue: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: Loko Kung <lokokung@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

generator/dawn_version_generator.py

@@ -127,13 +127,12 @@ class DawnVersionGenerator(Generator):
         if version_file:
             return [version_file]
         if git_exists(dawn_dir):
-            deps = []
             try:
-                deps += [get_git_head(dawn_dir)
+                return [get_git_head(dawn_dir)
                         ] + get_git_resolved_head(dawn_dir)
             except Exception:
-                return deps
-        return deps
+                return []
+        return []
 
     def get_file_renders(self, args):
         params = compute_params(args)