Some lousy BIOSes, e.g. my Aspire 5720 BIOS forget to restore the GUID
register on resume from RAM.

Fix that by setting it to the last value that was read from it.
Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>