x11-toolkits/fox17: fix build on armv7

The FXThread::ticks() polyfill had a wrong type name, presumably
as it isn't used on common 64 bit platforms.

Approved by: portmgr (build fix blanket)
MFH: 2025Q2

(cherry picked from commit c05f77799d7a04d31098db52bfad3f71cf366f49)