Fix some BLS snippets not being displayed in the GRUB menu
There was an error in the logic that stored the parsed BLS snippets in the
sorted linked list that is used to populate the GRUB boot menu entries.
Also add a fix found by coverity scan about a possible undefined behaviour
due grub_efi_status_t having the wrong type.
Signed-off-by: Javier Martinez Canillas <email@example.com>