[ot_certs] Fix typo in error string

Signed-off-by: Amaury Pouly <[email protected]>

sw/host/ot_certs/src/asn1/der.rs

@@ -67,7 +67,7 @@ impl Der {
         match val {
             Value::Literal(x) => Ok(x),
             Value::Variable(Variable { name, .. }) => bail!(
-                "cannot push value of variable {name}: the Der generator does not support literals"
+                "cannot push value of variable {name}: the DER generator does not support variables"
             ),
         }
     }