crypto: jitterentropy - use safe format string parameters

Since the API for jent_panic() does not include format string parameters,
adjust the call to panic() to use a literal string to avoid any future
callers from leaking format strings into the panic message.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>