Check subkey id instead of masterkey id on security token operations

Rename ambiguous getMasterKeyFingerprint -> getKeyFingerprint

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/SecurityTokenHelper.java

@@ -22,6 +22,8 @@
 
 package org.sufficientlysecure.keychain.securitytoken;
 
+import android.support.annotation.NonNull;
+
 import org.bouncycastle.bcpg.HashAlgorithmTags;
 import org.bouncycastle.util.Arrays;
 import org.bouncycastle.util.encoders.Hex;
@@ -131,13 +133,13 @@ public class SecurityTokenHelper {
     private boolean isSlotEmpty(KeyType keyType) throws IOException {
         // Note: special case: This should not happen, but happens with
         // https://github.com/FluffyKaon/OpenPGP-Card, thus for now assume true
-        if (getMasterKeyFingerprint(keyType) == null) return true;
+        if (getKeyFingerprint(keyType) == null) return true;
 
         return keyMatchesFingerPrint(keyType, BLANK_FINGERPRINT);
     }
 
     public boolean keyMatchesFingerPrint(KeyType keyType, byte[] fingerprint) throws IOException {
-        return java.util.Arrays.equals(getMasterKeyFingerprint(keyType), fingerprint);
+        return java.util.Arrays.equals(getKeyFingerprint(keyType), fingerprint);
     }
 
     /**
@@ -723,10 +725,10 @@ public class SecurityTokenHelper {
      * Return the fingerprint from application specific data stored on tag, or
      * null if it doesn't exist.
      *
-     * @param keyType key.operatio type
+     * @param keyType key type
      * @return The fingerprint of the requested key, or null if not found.
      */
-    public byte[] getMasterKeyFingerprint(KeyType keyType) throws IOException {
+    public byte[] getKeyFingerprint(@NonNull KeyType keyType) throws IOException {
         byte[] data = getFingerprints();
         if (data == null) {
             return null;