MAINTAINERS: powerpc: Mark Maddy as "M"

Mark Maddy as a co-maintainer, so that he can get a kernel.org account
and help manage the powerpc tree on kernel.org.

Acked-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241115045442.675721-1-mpe@ellerman.id.au

Author: mpe

MAINTAINERS

@@ -13106,7 +13106,7 @@ M:	Michael Ellerman <mpe@ellerman.id.au>
 R:	Nicholas Piggin <npiggin@gmail.com>
 R:	Christophe Leroy <christophe.leroy@csgroup.eu>
 R:	Naveen N Rao <naveen@kernel.org>
-R:	Madhavan Srinivasan <maddy@linux.ibm.com>
+M:	Madhavan Srinivasan <maddy@linux.ibm.com>
 L:	linuxppc-dev@lists.ozlabs.org
 S:	Supported
 W:	https://github.com/linuxppc/wiki/wiki