syscall: fix riscv64 GNU/Linux build

Make syscall_linux_riscv64.go, new in the 1.14beta1 release, look like
the other syscall_linux_GOARCH.go files.

Change-Id: Icc79540e886cefbda376a98b5c37dcb26e48ecbc
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/217577
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed