util: Fix gcn-gpu docker download to v21-2

Change-Id: Ibb64d080dc72c7208c97a5272d443a17122ab60b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54468
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed