veriexec(4): Fix a compiler error

When building WITH_BEARSSL=1 veriexec(4) failes to compile.
So update the function prototype so that veriexec(4)
compiles again.

Reported by: gbe
Reviewed by: mjg, gbe
Approved by: mjg
Pull Request: https://github.com/freebsd/freebsd-src/pull/657

(cherry picked from commit 7e2af4f90bb1dca907ce024324b1e64c48ca4472)