nvramtool: write size field more obviously

The field wasn't initialized in RAM first and later overwritten in a somewhat
twisted way (that relied on the size field coming after the tag field in the
struct).

Change-Id: Ibe931b297df51e3c46ae163e059338781f5a27e2
Found-by: Coverity Scan
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/4087
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)
diff --git a/util/nvramtool/accessors/layout-bin.c b/util/nvramtool/accessors/layout-bin.c
index fd3e08c..4b7f8d6 100644
--- a/util/nvramtool/accessors/layout-bin.c
+++ b/util/nvramtool/accessors/layout-bin.c
@@ -112,6 +112,7 @@
 			sum += sizeof(table);
 			table.header_length = sizeof(table);
 			table.tag = LB_TAG_CMOS_OPTION_TABLE;
+			table.size = 0;
 
 			if (fwrite((char *)&table, sizeof(table), 1, f) != 1) {
 				perror("Error writing image file");
@@ -187,12 +188,13 @@
 		goto err;
 	}
 
-	if (fseek(f, sizeof(table.tag), SEEK_SET) != 0) {
+	if (fseek(f, 0, SEEK_SET) != 0) {
 		perror("Error while seeking");
 		goto err;
 	}
 
-	if (fwrite((char *)&sum, sizeof(table.tag), 1, f) != 1) {
+	table.size = sum;
+	if (fwrite((char *)&table, sizeof(table), 1, f) != 1) {
 		perror("Error writing image file");
 		goto err;
 	}