MAINTAINERS: Add a secondary maintainer for bluefield_edac

Add David as a secondary maintainer.

  [ bp: Rewrite commit message. ]

Signed-off-by: David Thompson <davthompson@nvidia.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250319181630.2673-1-davthompson@nvidia.com