mtree: Add missing sound entry for /usr/examples

Sponsored by: Beckhoff Automation GmbH & Co. KG

(cherry picked from commit af5e348c61dac360de7774fc0ecbf53ae056177c)

mtree: Fix entry

Fixes: af5e348c61da ("mtree: Add missing sound entry for /usr/examples")
(cherry picked from commit fee14577d59013f2277a4b0f4b2f4108e417e7c3)