MAINTAINERS: Also assign siwx91x drivers to Silabs

Usually, drivers for siwx91x are named "silabs_siwx91x". However, there
are a few exceptions:
  - **/Kconfig.siwx91x
  - drivers/wifi/siwx91x

Let's ensure the reviewers for these files are properly assigned.

Signed-off-by: Jérôme Pouiller <[email protected]>

Author: jerome-pouiller

MAINTAINERS.yml

@@ -3627,6 +3627,7 @@ Silabs Platforms:
     - drivers/*/*gecko*
     - drivers/bluetooth/hci/hci_silabs_*
     - drivers/*/*silabs*
+    - drivers/**/*siwx91x*
     - tests/boards/silabs/
   labels:
     - "platform: Silabs"