tools, fit_check_sign: verify a signed fit image

add host tool "fit_check_sign" which verifies, if a fit image is
signed correct.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
index 0fe6e9f..ca8c120 100644
--- a/lib/rsa/rsa-sign.c
+++ b/lib/rsa/rsa-sign.c
@@ -193,7 +193,7 @@
 		goto err_create;
 	}
 	EVP_MD_CTX_init(context);
-	if (!EVP_SignInit(context, checksum_algo->calculate())) {
+	if (!EVP_SignInit(context, checksum_algo->calculate_sign())) {
 		ret = rsa_err("Signer setup failed");
 		goto err_sign;
 	}