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

…tomatically (#18333)

#### Why I did it
src/sonic-linux-kernel
```
* b6fd1ba - (HEAD -> master, origin/master, origin/HEAD) arm64: dts: marvell: Add DTS for 7215-IXS-A1 board (#378) (4 hours ago) [Pavan-Nokia]
* bab1510 - Disable small sector erase size for UBIFS on flash (#382) (8 hours ago) [Mridul Bajpai]
```
#### How I did it
#### How to verify it
#### Description for the changelog