rng: also pretty print configuration errors

If the parsed commandline options cannot be converted into a
`VuRngConfig` we would only get a .unwrap() error message.

Chain this before the check of the daemon launch.

Suggested-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Erik Schilling <erik.schilling@linaro.org>

crates/rng/src/main.rs

@@ -170,7 +170,7 @@ pub(crate) fn start_backend(config: VuRngConfig) -> Result<()> {
 fn main() {
     env_logger::init();
 
-    if let Err(e) = start_backend(VuRngConfig::try_from(RngArgs::parse()).unwrap()) {
+    if let Err(e) = VuRngConfig::try_from(RngArgs::parse()).and_then(start_backend) {
         error!("{e}");
         exit(1);
     }