uefi: Fix encoding the GUID into the capsule EFI variable
uefi: Fix encoding the GUID into the capsule EFI variable

Before:

$ /usr/lib/fwupd/fwupdate --info
Information for the update status entry 0:
  Information Version: 7
  Firmware GUID: {00000000-0000-0000-0000-000000000000}
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Capsule Flags: 0x00131072x
  Hardware Instance: 0
  Update Status: attempt-update
  Capsule File Path: /EFI/ubuntu/fw/fwupd-7ceaf7a8-0611-4480-9e30-64d8de420c7c.cap

After:

$ /usr/lib/fwupd/fwupdate --info
Information for the update status entry 0:
  Information Version: 7
  Firmware GUID: {7ceaf7a8-0611-4480-9e30-64d8de420c7c}
  Capsule Flags: 0x00131072x
  Hardware Instance: 0
  Update Status: attempt-update
  Capsule File Path: /EFI/ubuntu/fw/fwupd-7ceaf7a8-0611-4480-9e30-64d8de420c7c.cap

fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,vathpela/fwupd,fwupd/fwupd