ssh/tailssh: fix gokrazy SSH crash

Stupid mistake in earlier refactor.

Updates gokrazy/gokrazy#209

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ssh/tailssh/user.go

@@ -59,12 +59,14 @@ func userLookup(username string) (*userMeta, error) {
 	if distro.Get() == distro.Gokrazy {
 		um, err := userLookupStd(username)
 		if err != nil {
-			um.User = user.User{
+			um = &userMeta{
+				User: user.User{
 					Uid:      "0",
 					Gid:      "0",
 					Username: "root",
 					Name:     "Gokrazy",
 					HomeDir:  "/",
+				},
 			}
 		}
 		um.loginShellCached = "/tmp/serial-busybox/ash"