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

MAINTAINERS

@@ -8214,6 +8214,7 @@ F:	drivers/edac/aspeed_edac.c
 
 EDAC-BLUEFIELD
 M:	Shravan Kumar Ramani <shravankr@nvidia.com>
+M:	David Thompson <davthompson@nvidia.com>
 S:	Supported
 F:	drivers/edac/bluefield_edac.c