MAINTAINERS: erofs: Add Documentation/ABI/testing/sysfs-fs-erofs

Add this doc to the erofs maintainers entry.
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230209052013.34952-1-frank.li@vivo.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

MAINTAINERS

@@ -7744,6 +7744,7 @@ R:	Jeffle Xu <jefflexu@linux.alibaba.com>
 L:	linux-erofs@lists.ozlabs.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
+F:	Documentation/ABI/testing/sysfs-fs-erofs
 F:	Documentation/filesystems/erofs.rst
 F:	fs/erofs/
 F:	include/trace/events/erofs.h