Make EMPTY_KEY static.

Co-authored-by: Martin Balao Alonso <[email protected]>
Co-authored-by: Francisco Ferrari Bihurriet <[email protected]>

src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/P11KDF.java

@@ -43,7 +43,7 @@ final class P11KDF extends KDFSpi {
     private final Token token;
     private final P11SecretKeyFactory.HKDFKeyInfo svcKi;
     private final long hmacMechanism;
-    private final SecretKey EMPTY_KEY = new SecretKey() {
+    private static final SecretKey EMPTY_KEY = new SecretKey() {
         @Override
         public String getAlgorithm() {
             return "Generic";