vendorcode/amd/pi/Lib: Fix reporting fatal error

Instead of writing the first word of 6 "post code structs" where only
one exists (leading to 0xDEAD and 5 garbage words), write the correct
set.

Change-Id: Ifdfa53a970dda33dc9dc8c05788875077c001ecf
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Found-by: Coverity Scan #1361054, #1361055, #1361056
Reviewed-on: https://review.coreboot.org/16058
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/vendorcode/amd/pi/Lib/amdlib.c

@@ -1408,7 +1408,7 @@ IdsErrorStop (
 
 	while(1) {
 		offset %= sizeof(struct POST) / 2;
-		WriteIo32(80, *((UINT32*)(&post+offset)));
+		WriteIo16(80, *((UINT16 *)&post)+offset);
 		++offset;
 		for (j=0; j<250; ++j) {
 			ReadIo8(80);