stub: override StubInfo EFI variable unconditionally, since *we* own it

The other variables are owned by the boot menu (i.e. sd-boot), we only
fill those in if it didn't do so for us (to support cases where our stub
kernel is directly invoked by UEFI). But StubInfo is genuinely about the
stub, hence let's simplify things and unconditionally set it from the
stub.

src/boot/efi/stub.c

@@ -142,9 +142,9 @@ static void export_variables(EFI_LOADED_IMAGE_PROTOCOL *loaded_image) {
                 efivar_set(LOADER_GUID, L"LoaderFirmwareType", s, 0);
         }
 
-        /* add StubInfo */
-        if (efivar_get_raw(LOADER_GUID, L"StubInfo", NULL, NULL) != EFI_SUCCESS)
-                efivar_set(LOADER_GUID, L"StubInfo", L"systemd-stub " GIT_VERSION, 0);
+        /* add StubInfo (this is one is owned by the stub, hence we unconditionally override this with our
+         * own data) */
+        (void) efivar_set(LOADER_GUID, L"StubInfo", L"systemd-stub " GIT_VERSION, 0);
 }
 
 EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *sys_table) {