MAINTAINERS: aspeed: Update git tree URL

The description for joel/aspeed.git on git.kernel.org currently says:

    Old Aspeed tree. Please see joel/bmc.git

Let's update MAINTAINERS accordingly.
Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230922223405.24717-2-zev@bewilderbeest.netSigned-off-by: Joel Stanley <joel@jms.id.au>

MAINTAINERS

@@ -1968,7 +1968,7 @@ L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 L:	linux-aspeed@lists.ozlabs.org (moderated for non-subscribers)
 S:	Supported
 Q:	https://patchwork.ozlabs.org/project/linux-aspeed/list/
-T:	git git://git.kernel.org/pub/scm/linux/kernel/git/joel/aspeed.git
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/joel/bmc.git
 F:	Documentation/devicetree/bindings/arm/aspeed/
 F:	arch/arm/boot/dts/aspeed/
 F:	arch/arm/mach-aspeed/