blobs/download: try backup if bad hash on main

At present, the logic only tries backup URLs when an
actual download fails (bad internet connection or the
server is down).

If the main download succeeds, but it has a bad checksum,
the backup download is not attempted.

Since wrongly hashed files are to be assumed useless, we
may aswell delete and try the next file. This will guard
against the possibility of a vendor changing their file,
without changing the file name (non-versioned files, for
example, may be subject to such changes).

Signed-off-by: Leah Rowe <leah@libreboot.org>

resources/scripts/update/blobs/download

@@ -452,12 +452,20 @@ fetch_update()
 	dl_path=${blobdir}/cache/${dlsum}
 	mkdir -p ${blobdir}/cache
 
-	vendor_checksum ${dlsum} || \
-		wget -U "${agent}" ${dl} -O ${dl_path} \
-		|| wget -U "${agent}" ${dl_bkup} -O ${dl_path}
-
-	vendor_checksum ${dlsum} || fail \
-		"Cannot guarantee intergity of vendor update for: ${board}"
+	dl_fail="y"
+	vendor_checksum ${dlsum} && dl_fail="n"
+	for x in "${dl}" "${dl_bkup}"; do
+		if [ "${dl_fail}" = "n" ]; then
+			break
+		fi
+		rm -f "${dl_path}"
+		wget -U "${agent}" ${x} -O ${dl_path}
+		vendor_checksum ${dlsum} && dl_fail="n"
+	done
+	if [ "${dl_fail}" = "y" ]; then
+		printf "Could not download blob file\n" 1>&2
+		return 1
+	fi
 }
 
 vendor_checksum()