MAINTAINERS: add maple tree mailing list

There is a mailing list for the maple tree development.  Add the list to
the maple tree entry of the MAINTAINERS file so patches will be sent to
interested parties.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liam R. Howlett <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: howlett

MAINTAINERS

@@ -12481,6 +12481,7 @@ F:	net/mctp/
 
 MAPLE TREE
 M:	Liam R. Howlett <[email protected]>
+L:	[email protected]
 L:	[email protected]
 S:	Supported
 F:	Documentation/core-api/maple_tree.rst