mnt_idmapping: Use kmemdup_array instead of kmemdup for multiple allocation

Let the kememdup_array() take care about multiplication and possible
overflows.

v2:Add a new modification for reverse array.

Signed-off-by: Yu Jiaoliang <yujiaoliang@vivo.com>
Link: https://lore.kernel.org/r/20240823015542.3006262-1-yujiaoliang@vivo.com


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>