MAINTAINERS: include linux-mm for xarray maintenance

MM developers have an interest in the xarray code.

Cc: David Gow <davidgow@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

MAINTAINERS

@@ -25729,6 +25729,7 @@ F:	arch/x86/entry/vdso/
 XARRAY
 M:	Matthew Wilcox <willy@infradead.org>
 L:	linux-fsdevel@vger.kernel.org
+L:	linux-mm@kvack.org
 S:	Supported
 F:	Documentation/core-api/xarray.rst
 F:	include/linux/idr.h