fmap: Fix length calculation in error message

Change-Id: Ie0f448970de6a7829f304448e0835eaeb7d103a3
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/30152
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
diff --git a/fmap.c b/fmap.c
index d44b7fa..84b3b54 100644
--- a/fmap.c
+++ b/fmap.c
@@ -243,7 +243,7 @@
 			if (flashctx->chip->read(flashctx, (uint8_t *)fmap + sig_len,
 						offset + sig_len, sizeof(*fmap) - sig_len)) {
 				msg_cerr("Cannot read %zu bytes at offset %06zx\n",
-						sizeof(*fmap) + sig_len, offset + sig_len);
+						sizeof(*fmap) - sig_len, offset + sig_len);
 				continue;
 			}