crypto: fix nettle config check for running pbkdf test

The pbkdf test is being built based on a check for CONFIG_NETTLE.
As of fff2f982ab6ac0dd2b641d30303f72270a019f28, it should be
instead checking CONFIG_NETTLE_KDF

Reported-by: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Tested-by: Bruce Rogers <brogers@suse.com>
Tested-by: Ed Maste <emaste@freebsd.org>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/tests/Makefile b/tests/Makefile
index 45b9048..651d8b2 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -92,7 +92,7 @@
 check-unit-y += tests/test-io-channel-command$(EXESUF)
 check-unit-y += tests/test-io-channel-buffer$(EXESUF)
 check-unit-y += tests/test-base64$(EXESUF)
-check-unit-$(if $(CONFIG_NETTLE),y,$(CONFIG_GCRYPT_KDF)) += tests/test-crypto-pbkdf$(EXESUF)
+check-unit-$(if $(CONFIG_NETTLE_KDF),y,$(CONFIG_GCRYPT_KDF)) += tests/test-crypto-pbkdf$(EXESUF)
 check-unit-y += tests/test-crypto-ivgen$(EXESUF)
 check-unit-y += tests/test-crypto-afsplit$(EXESUF)
 check-unit-y += tests/test-crypto-xts$(EXESUF)