Use correct clang-format in BUILD.gn

The bot was broken in https://skia-review.googlesource.com/c/27800/
Depot Tools' version is just a wrapper which looks for clang-format
under buildtools, which doesn't exist on the bots.

Bug: skia:6893
Change-Id: I32ae6c358735c9971e533064aa50a0e0520dd05a
Reviewed-on: https://skia-review.googlesource.com/28020
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index b772056..5b06c17 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -456,7 +456,7 @@
     }
     args = [
       rebase_path(skslc_path),
-      rebase_path("infra/bots/.recipe_deps/depot_tools/clang-format"),
+      rebase_path("bin/clang-format"),
     ]
     args += rebase_path(skia_gpu_processor_sources)
   }