multimedia/vvenc: fix build on armv7

No SIMD on armv7, but there's one place in the code where they forgot
to check if we want SIMD or not. Fix the oversight to make the port
work.

Approved by: portmgr (build fix blanket)
MFH: 2023Q4

(cherry picked from commit 3db813ec767819d1b3936d8bac1d08b3549f404d)