rsa: check that pointer checksum isn't NULL before using it

The pointer checksum were used before checking that it
isn't NULL. We move the code that use it after the check.

Reported-by: Coverity (CID: 185835)
Signed-off-by: NPhilippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

lib/rsa/rsa-verify.c

@@ -295,7 +295,7 @@ static int rsa_verify_key(struct image_sign_info *info,
 #endif
 	struct checksum_algo *checksum = info->checksum;
 	struct padding_algo *padding = info->padding;
-	int hash_len = checksum->checksum_len;
+	int hash_len;
 
 	if (!prop || !sig || !hash || !checksum)
 		return -EIO;
@@ -315,6 +315,7 @@ static int rsa_verify_key(struct image_sign_info *info,
 	}
 
 	uint8_t buf[sig_len];
+	hash_len = checksum->checksum_len;
 
 #if !defined(USE_HOSTCC)
 	ret = uclass_get_device(UCLASS_MOD_EXP, 0, &mod_exp_dev);