MAINTAINERS: Mark Andrew as M: for ASPEED MACHINE SUPPORT

From discussion in [1] and in-person with Joel, flip my entry from R:
to M:.

Link: https://lore.kernel.org/all/CACPK8Xe8yZLXzEQPp=1D2f0TsKA7hBZG=pHHW6U51FMpp_BiRQ@mail.gmail.com/

 [1]
Cc: Joel Stanley <joel@jms.id.au>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: soc@lists.linux.dev
Cc: linux-aspeed@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Acked-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>