fixed missing dependency in spirv-tools/BUILD.gn

Change-Id: Ib0381e2bc10649e62d3fb8ddfc34be46537a2e5b
Reviewed-on: https://skia-review.googlesource.com/9804
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed