efi_loader: pass GUIDs as const efi_guid_t *

efi_loader: pass GUIDs as const efi_guid_t *

We need to call some boottime services internally.
Our GUIDs are stored as const efi_guid_t *.

The boottime services never change GUIDs.
So we can define the parameters as const efi_guid_t *.

Signed-off-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>