dashboard: fix ssh username for ppc64le-power9 builder

Updates golang/go#34739

Change-Id: I6499ff6a0e1885fad3a5f5ba7c1fa4e0113e716c
Reviewed-on: https://go-review.googlesource.com/c/build/+/200398
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 661a05fc..4579b0f 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -430,7 +430,7 @@
 		IsReverse:       true,
 		env:             []string{"GOROOT_BOOTSTRAP=/usr/local/go-bootstrap"},
 		ReverseAliases:  []string{"linux-ppc64le-power9osu"},
-		SSHUsername:     "debian",
+		SSHUsername:     "root",
 		HermeticReverse: false, // TODO: use rundockerbuildlet like arm64
 	},
 	"host-linux-arm64-packet": &HostConfig{