casviewer: fix build
casviewer: fix build

This is follow up for
https://crrev.com/c/2684031

Bug: 1172879
Change-Id: I9a71733067a4e26195b81a825c61d7d01245a272
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2684059
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go