MAINTAINERS: add myself rghaddab to collaborators of Flash

Add myself to the collaborator list of flash to contribute to the work
of enhancement of flash API

Signed-off-by: Riadh Ghaddab <[email protected]>

Author: rghaddab

MAINTAINERS.yml

@@ -1397,6 +1397,8 @@ Release Notes:
   status: maintained
   maintainers:
     - de-nordic
+  collaborators:
+    - rghaddab
   files:
     - drivers/flash/
     - dts/bindings/flash_controller/