[submodule] Update submodule sonic-linux-kernel to the latest HEAD au…

…tomatically (sonic-net#17231)

#### Why I did it
src/sonic-linux-kernel
```
* 6ff3cc2 - (HEAD -> 202305, origin/202305) arm64: Kconfig inclusions to fix PCI hang and MTD detection (sonic-net#362) (2 days ago) [Pavan Naregundi]
```
#### How I did it
#### How to verify it
#### Description for the changelog