xarray: Add MAINTAINERS entry

Add myself as XArray and IDR maintainer.
Signed-off-by: Matthew Wilcox <willy@infradead.org>

MAINTAINERS

@@ -15973,6 +15973,17 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/vdso
 S:	Maintained
 F:	arch/x86/entry/vdso/
 
+XARRAY
+M:	Matthew Wilcox <willy@infradead.org>
+L:	linux-fsdevel@vger.kernel.org
+S:	Supported
+F:	Documentation/core-api/xarray.rst
+F:	lib/idr.c
+F:	lib/xarray.c
+F:	include/linux/idr.h
+F:	include/linux/xarray.h
+F:	tools/testing/radix-tree
+
 XC2028/3028 TUNER DRIVER
 M:	Mauro Carvalho Chehab <mchehab@kernel.org>
 L:	linux-media@vger.kernel.org