MAINTAINERS: replace a Microchip AT91 maintainer

As Ludovic is more focusing on other aspects of the Microchip
Linux-based development, replace him with Claudiu.
Entry is added to the CREDITS file.

Thanks Ludovic for these great contributions in the kernel space!

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Link: https://lore.kernel.org/r/23819d8baa635815d0893955197561fe4f044d5e.1643553501.git.nicolas.ferre@microchip.com