riscv: fix riscv64sf build

The library needs to have sf suffix cut off.

Differential revision: https://reviews.freebsd.org/D34561
Reviewed by: dim
Approved by: re (gjb)

(cherry picked from commit 18f71c9b2779999a9492b42c325524651a1b6909)
(cherry picked from commit 78e68a3d10216db2b3a6ddb0d4591358987c033e)