RFR 8157544: Typo in CtrDrbg::toString

[Wang Weijun]

Once upon a time securerandom.drbg.config looks like "Hash_DRBG/SHA-256" and it 
was changed to "Hash_DRBG,SHA-256" because "Hash_DRBG/SHA-512/224" is ambiguous.

DRBG::toString follows this style, but I forgot to update one case.

Now, it is fixed.

     @Override
     public String toString() {
-        return super.toString() + "/"
+        return super.toString() + ","
                 + (usedf ? "use_df" : "no_df");
     }

No webrev, just the patch above. Please take a review.

Thanks
Max