entropy source: missed useed ref in appendix

 On branch dev/next-release
 Your branch is up-to-date with 'origin/dev/next-release'.

 Changes to be committed:
	modified:   doc/scalar/riscv-crypto-scalar-appx-entropy-source.adoc

 Changes not staged for commit:
	modified:   extern/riscv-gnu-toolchain (modified content)
	modified:   extern/sail-riscv (untracked content)