l3afpad: Add missing mime-xdg inherit
Fixes:
WARNING: l3afpad-0.8.18.1.11+gitAUTOINC+3cdccdc950-r0 do_package_qa: QA Issue:
package contains desktop file with key 'MimeType' but does not inhert mime-xdg:
l3afpad path 'XXX/packages-split/l3afpad/usr/share/applications/l3afpad.desktop' [mime-xdg]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>