multimedia/mpv: unbreak system-wide configs after 1d89ec25be62

$ mpv -v -v 2>&1 | fgrep etc
[global] config path: 'encoding-profiles.conf' -/-> 'etc/mpv/encoding-profiles.conf'
[global] config path: 'mpv.conf' -/-> 'etc/mpv/mpv.conf'
[global] config path: 'config' -/-> 'etc/mpv/config'
[global] config path: 'input.conf' -/-> 'etc/mpv/input.conf'
[global] config path: 'script-opts/ytdl_hook.conf' -/-> 'etc/mpv/script-opts/ytdl_hook.conf'
[global] config path: 'lua-settings/ytdl_hook.conf' -/-> 'etc/mpv/lua-settings/ytdl_hook.conf'
[global] config path: 'script-opts/stats.conf' -/-> 'etc/mpv/script-opts/stats.conf'
[global] config path: 'lua-settings/stats.conf' -/-> 'etc/mpv/lua-settings/stats.conf'
[global] config path: 'script-opts/console.conf' -/-> 'etc/mpv/script-opts/console.conf'
[global] config path: 'lua-settings/console.conf' -/-> 'etc/mpv/lua-settings/console.conf'
[global] config path: 'script-opts/osc.conf' -/-> 'etc/mpv/script-opts/osc.conf'
[global] config path: 'lua-settings/osc.conf' -/-> 'etc/mpv/lua-settings/osc.conf'