Fix update_kernel.sh and update 6.1 kernel

Issue with `COS_KERNEL`:

```
./update_kernel.sh: line 37: /usr/local/google/home/zizhengwu/cos/src/overlays/project-edgeos/sys-kernel/lakitu-kernel-6_1/../../../project-lakitu/sys-kernel/lakitu-kernel-6_1/: Is a directory
```

Issue with `COS_EBUILD_VERSION`:

```
+ COS_EBUILD_VERSION='
6.1.80
'
+ ln -s 'lakitu-kernel-6_1-
6.1.80
.ebuild' 'lakitu-kernel-6_1-
6.1.80
-r21.ebuild'
```

BUG=b/273286671
TESTED=`emerge-gmec-amd64-hw sys-kernel/lakitu-kernel-6_1`
RELEASE_NOTE=n/a

Change-Id: Ie300db6532e1e9b64ef522b2260ca64400dadd4c
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/68416
Reviewed-by: Alan Berryhill <berryhill@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
7 files changed