[RISCV] Fix non-sensical intrinsic names in rv64i-single-softfloat.ll. NFC

Many of these had an extra 'f' at the beginning of their name that
caused them to not be treated as intrinsics.

I'm not sure what fpround was supposed to be so I deleted it.

frem was changed from an intrinsic to an instruction.

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D113528