test: sandbox: fix link error with do_ut_bootm if BLOBLIST=n

Having CONFIG_OF_EMBED=y && CONFIG_BLOBLIST=n leads to the link
error:
```
ld: /tmp/ccwtRVty.ltrans28.ltrans.o:(.data.rel+0x4e8): undefined \
                                            reference to `do_ut_bootm'
```

Fixes: fe158657a5b ("test: inconsistent bootm tests")
Signed-off-by: Evgeny Bachinin <EABachinin@salutedevices.com>
1 file changed