cmd/compile: regenerate rewriteRISCV64.go to match cl 528975

cmd/compile: regenerate rewriteRISCV64.go to match cl 528975

The final revision of

https://go-review.googlesource.com/c/go/+/528975

made a small change to the RISCV64.rules file but neglected to update
the regenerated rewriteRISCV64.go file.

Change-Id: I04599f4e3b0dac7102c54166c9bae6fc9b6621d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/533815
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>