dts: fix MULTI_DTB_FIT compression choice prompt

This choice is not about SPL for which we have a separate choice.

Fixes: 95f4bbd5 ("lib: fdt: Allow LZO and GZIP DT compression in U-Boot")
Cc: Marek Vasut <marek.vasut+renesas@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>